Copyright

William Collins

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This eBook first published in Great Britain by William Collins in 2019

Copyright © Dan Eatherley 2019

Nineteenth-century engravings on chapter title pages are © Shutterstock, with the exception of chapter 6, which is © ilbusca / Getty Images

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Source ISBN: 9780008262747

eBook Edition © June 2019 ISBN: 9780008262761

Version: 2019-05-28

Dedication

To Georgia

Epigraph

‘Turkeys, carps, hops, pickerel, and beer,

Came into England all in one year.’

Chronicle of the Kings of England

unto the Death of King James, Sir Richard Baker, 1643

Contents

Cover

Title Page

Copyright

Dedication

Epigraph

Prologue

1 Ecological Explosions

2 First Invaders

3 Romans and Normans

4 New Worlds, New Invaders

5 The Empire Strikes Back

6 The Plant Hunters

7 Unwanted Hitch-Hikers

8 Fur Farm

9 Freshwater Invaders

10 Underneath the Waves

11 Fighting Fire with Fire

12 The Future

Further Reading

Index of Species

General Index

Acknowledgements

About the Book

About the Author

About the Publisher

Prologue
A Hornet’s Nest

Tetbury, Gloucestershire. 2.30 pm. Wednesday 28 September 2016

The wind had strengthened again and was blowing in short, powerful flurries. Graham paced up and down, his attention focused on the boundary hedges. Drawn by reports of sightings in the area, the team had last week netted several specimens of the invader that had been hawking for prey on ivy clinging to the trunk of one of the garden’s cypresses. A reliable line of sight had been achieved and further samples dispatched for DNA analysis. But that had been all.

Graham approached the conifer once more. No activity here today. As he turned back though, something danced in his peripheral vision, something way up in the cypress closest to the house. Was it his imagination? He squinted for a better look. Sure enough, four, five, maybe six, large-ish insects were whirling about the highest branches.

What the heck were they doing? What on earth was interesting them up there?

Not yet daring to hope, he reached for his binoculars. Within moments Graham confirmed the target species and shouted over to his colleague.

‘Hey Gordon! This could be it!’

Confidence building, Graham scanned the canopy for a few seconds, but saw only thick evergreen branches whipping and twisting in the wind. Frustrating. He stepped back a pace.

In that instant, a gust lifted the foliage enough to reveal a tell-tale patch of light brown against the darker trunk. Had he been standing a foot to the left or right, he would have seen nothing. It was just a glimpse, but now he was certain and made the call to the command centre: ‘I think we’ve found the nest.’ All Graham could do now was wait. And pray he was right.

The National Bee Unit – a division of APHA, the British government’s Animal and Plant Health Agency – has long expected this unwelcome visitor from the far side of the planet. Back home the Asian hornet is on the move, pushing from its native range, on the border of northern India and China, into Indonesia and South Korea. Soon Japan, too, will succumb. The species was confirmed in Europe as early as 2004 when a nest was discovered close to Agen in southwest France. No one really knows how it got there. The best guess is that a year or two earlier some fertile queens had been inadvertently shipped to Bordeaux in a container-load of ceramic pottery from eastern China.

The hornet found the temperate European conditions, similar to those back home, to its liking. Competition from local hornets was minimal – the Asian variety is smaller than its native counterpart, more like a very large wasp; and far quieter. (Experts say the chug-chug-chug of an approaching European hornet calls to mind a lumbering Chinook helicopter. If so, the newcomer is a Stealth fighter.) And it relished the plentiful supply of food in the shape of other aerial insects. This is where the problem lies, for while the Asian hornet is partial to hoverflies, wasps and various types of wild bee, it really goes to town on the honeybee, swooping in on hives to pluck off its far smaller quarry. With a (compound) eye on efficiency, worker hornets behead their prey then dismember it, biting off the wings, legs and abdomen, before taking back to the nest only the thorax, stuffed with protein-rich flight muscles – perfect fodder for the developing hornet brood. It’s the entomological equivalent of a shopping trip for prime rump steak, except the hornets do their own butchery.

In the worst cases, mobs of hornets will linger at the hive entrance, decapitating the emerging bees one after the other until they can move into the colony unchallenged, stripping it of honey, eggs and larvae. The bees back in Asia cobble together a defence of sorts, carpeting the hive entrance and swamping the intruders in a mass of shimmering abdomens. The heat-ball produced by the friction is enough to cook the intruder. The European bees have a go at this too but seem far less effective.

With the deck stacked in its favour, the Asian hornet has a field day. Over the summer, a single queen produces up to 6,000 young, almost ten times as many as typically found in a European hornet’s nest. Most offspring develop into sterile worker females – the ones wreaking the damage to bee colonies – but around 900 turn into breeding males and 350 become reproductive females, known as gynes, which form the next generation of queens. While many gynes either fail to mate or perish over the winter, a few survive to start new nests themselves the following year. It needs but a handful of these foundresses to succeed for a population to take off, particularly if the new nests aren’t detected and destroyed fast enough.

And that’s what happened in France. When nests were discovered in built-up areas, local firefighters were called in to remove them, but otherwise the authorities ignored the hornet, perhaps reassured by its lack of obvious threat towards humans. The insect isn’t especially aggressive and its sting no worse than that of the native hornet; in Europe perhaps a half-dozen fatalities to date can be attributed to Asian hornets – a statistic which compares favourably to deaths from wasp stings.

The honeybee population is less immune: in the Gironde département almost a third of colonies have been weakened or destroyed in a single year, one beekeeper losing 80 per cent of his hives. Dispersing at up to 80 kilometres each year – much further if the foundresses happen to hitch a ride in a passing vehicle – the Asian hornets have advanced unchecked over France. Along the way they have acquired a weakness for seafood, buzzing up and down coastal fish markets in search of small shrimps. It seems that any protein will do. By 2014, they had spread to Belgium, Portugal and Italy. One million of them were estimated to be in Germany. Then, in the early summer of 2016, they were spotted on the Channel Islands of Jersey and Alderney. It was only a matter of time before they reached the British mainland.

Changing agricultural practices going back a century have devastated Britain’s native bee and wasp populations, wiping out dozens of wild species and putting paid to many a honeybee colony. In recent decades, the threat to these important pollinators has worsened as crops have been drenched in pesticides and diseases have spread. Throw into the mix an exquisitely proficient bee-killer, and things have gone from bad to catastrophic.

For this reason, the UK government has adopted a zero-tolerance approach. The overriding objective of the Asian hornet response plan, the first of its kind in Europe, is the rapid interception and destruction of the insects before they get established. Beekeepers throughout the land are now on high alert, a select few tasked with active surveillance for the hornet, their colonies designated ‘sentinel’ apiaries. Meanwhile, members of the public are being encouraged to report, including via a mobile phone app, potential sightings of the visually distinctive invader. Unlike the native hornet, which sports a lively pattern of yellows and chestnuts on a dark-brown background, the Asian species is mostly black, save for a band of gold across the fourth segment of its abdomen. Added to that, it looks as if it’s waded knee-high through a puddle of yellow paint. Until now, none of the thousand-plus sightings, routed to the National Bee Unit (located at Sand Hutton, just outside York) for confirmation, have proved positive. But vigilance is key and government-funded bee inspectors are on the front line. A contingency plan – regularly field-tested – is in place. But before it can be executed, a positive identification is needed. In other words, someone has to catch a specimen.

Tuesday 20 September 2016

‘KILLER ASIAN HORNET INVASION’

‘SWARMS OF VICIOUS HORNETS SET TO HEAD TO BRITAIN’

‘MILITARY-STYLE OPERATION SPARKED TO DESTROY NESTS’

‘BRITONS WARNED OF DEADLY ASIAN HORNETS THAT CAN KILL FIFTY BEES A DAY’

The newspaper headlines that morning were typically understated. But they raised public awareness, and that was the point. In a press release issued the night before, the government confirmed that an Asian hornet had been identified in the Gloucestershire market town of Tetbury, and detailed the urgent steps that would form its rapid response to the invader. These included setting up a three-mile surveillance zone around the town, establishing a command centre at an undisclosed location and deploying bee inspectors to find the Asian hornet nest and pest control teams to destroy it. Emphasising the minimal threat to public safety posed by the hornets, Nicola Spence – the government’s top official for bee and plant health – nevertheless promised ‘swift and robust action’.

Monday 26 September 2016

The initial days of the operation proved frustrating. Each morning the inspectors were briefed before heading off in pairs to local apiaries armed with compasses, mobile phones to record grid references, binoculars and purpose-built hornet traps. At each site, the bee suit-clad inspectors hung around for a couple of hours hoping to spot hornets. The team worked off a list – provided by the Gloucestershire Beekeepers Association – which included apiaries at Prince Charles’s Highgrove estate and the Westonbirt arboretum. Some sites were located up to 20 kilometres from Tetbury, the initial surveillance zone having been extended. Perhaps the first sighting had been just the tip of the iceberg. Perhaps multiple nests were out there. But it soon became apparent that the team was wasting time at distant apiaries – the real action was happening less than a kilometre from the original discovery. And not at beehives.

‘I’m outside the Tesco’s,’ said one caller. ‘I’ve just seen some of those wasp-things.’ Sure enough, Asian hornets were confirmed buzzing about the red foliage of berberis hedging in the supermarket car park. More were clocked taking aphids from a willow coppice in a private garden nearby. And then this morning St Mary’s Primary School, in the centre of Tetbury, reported them on ivy in the playground, the area in question rapidly cordoned off as the inspectors went to work.

In predation mode, the hornets seemed oblivious to the fuss. They were not afraid of humans. They just carried on hawking. Inspectors could walk right up to them and stick them in a net. Keeping an eye on the insects as they flew off was trickier. At first, in the hope of improving the hornets’ visibility, the inspectors netted the insects, taped feathers to their abdomens and released them. But the hornets didn’t cooperate; instead they stopped at nearby trees to remove the cumbersome tags and zoomed off. The inspectors got their eye in eventually and abandoned the approach. It was not worth the hassle, you could see a hornet flying without a feather and get a good feel for the direction. After much perseverance, lines of sight were collected. The team was closing in.

One o’clock. Wednesday 28 September 2016

Graham Royle, a Cheshire-based seasonal bee inspector, had arrived in Tetbury the night before. He was among those providing relief to the 20-strong task force. More than 100 sites had been visited over the previous week, 50 traps deployed and dozens of fresh hornet sightings authenticated. A total of 94 separate observations would eventually be documented. Graham himself recorded a decent line of sight from a hedge that very morning, having trapped and released a hornet close to some ivy. Just before lunchtime, word came through from the command centre: ‘We’ve got an intersect.’

As it turned out, the flight lines – four or five good ones – which were plotted on a map didn’t converge neatly at one spot, but the criss-crossing did hint at a patch on the outskirts of Tetbury. Sixteen inspectors congregated in a car park. Teams of two, each provided with a map, started walking a section of this patch. It was not long afterwards that Graham, and fellow inspector Gordon Bull, found the nest. The garden with the cypress trees was a mere 600 metres from where the first hornet was spotted 23 days before.

Photos of the hornet’s nest were emailed for confirmation to Dr Quentin Rome at the Muséum National d’Histoire Naturelle in Paris – he has studied the Asian hornet’s advance with grim fascination for more than a decade. The nest was treated with a pesticide called Ficam B, an odourless white dust which is relatively harmless to humans but lethal to insects. Within an hour the nest was a mass grave.

The pumpkin-sized ball of chewed wood fibre was shipped to Sand Hutton for full analysis. The entire European population of Asian hornets belongs to just one of 13 subtypes known from the native range, implying a single introduction event, and genetic analysis later confirmed that the Tetbury hornets were of this same subtype. This suggested that they had indeed crossed the English Channel, rather than arriving independently from Asia. Further nests remained a possibility. Residents were asked to remain vigilant and bee inspectors would stay on for a further two weeks until the Tetbury outbreak was declared over.

Woolacombe, North Devon. One year later

As he did every day at this time of the year, retired physics teacher Martyn Hocking headed up the valley to visit his bees. At his back the mid-afternoon sun was still high over the sea. It was best to visit the apiary while the occupants were out and about: there would be fewer to deal with. He heard the hum before he saw the hives; right now, they were drowning in late summer bracken and barely visible.

Giving the first hive a generous blast from his smoker, he lifted the lid and administered a dose of sugar syrup. A large dark insect flitted past. Too big for a honeybee drone. The thing hovered for a moment, offering an unmistakable view of a yellow-orange band on an otherwise black abdomen. One of Martyn’s bees writhed in the grip of the larger insect, which seconds later darted off, vanishing into the emerald background as quickly as it had arrived.

1
Ecological Explosions

‘Let it be remembered how powerful the influence of a single introduced tree or mammal has been shown to be.’

On the Origin of Species, Charles Darwin, 1859

The 16 July 1898 edition of the Daily Mail devotes a single paragraph to the revelation that unusual creatures were on the loose in one of London’s better-heeled districts and defying all attempts at capture. According to the paper, ‘The wild animals on Hampstead Heath have just received an unexpected addition in the shape of two monkeys which have escaped from custody and are now enjoying a free and open life on the salubrious heights.’ A reward offered for the safe return of the simians – escaped pets from the nearby Bull and Bush tavern – proved unnecessary: a couple of days later the fugitives slunk back to the drinking house. Liberty hadn’t agreed with them. ‘They were in a deplorably dirty and woe-begone condition,’ as one account had it.

It turns out that Hampstead Heath, a windswept expanse on a sandy ridge to the north of the city, is no stranger to the exotic. In 1944, monkey business was again reported from the Heath, the arboreal frolics of a pair dubbed Jack and Jill causing disturbance on this occasion. Things didn’t end much better that time: Jill was shot and her dejected playmate handed himself in to the authorities. Then there was the young seal fished from a pond in 1926 having alarmed nocturnal anglers by ‘barking like a dog with a sore throat’. Other tales tell of a phantom gorilla, of giant spiders, of marauding bands of wild pigs.

For the people of London, the Heath is a little piece of countryside on their doorstep, an oasis in which to de-stress and reconnect with nature. Keats, Shelley, Wordsworth and Constable were among the many poets and artists in thrall to its bucolic charms, its wild and unspoilt landscapes. So precious is this place that the threat of quarrying and house-building prompted an 1871 Act of Parliament protecting for ever ‘the natural aspect and state of the Heath’.

But taking a stroll on the eastern end of the Heath one chilly autumnal morning in 2017, I was struck by just how much around me wasn’t ‘natural’ in the sense of representing native British fauna and flora. The most obvious example was the resident flock of a hundred or so ring-necked parakeets with their frequent shrill calls. With eyes closed, I could have been roaming a Darjeeling tea estate. The birds originate from sub-Saharan Africa and South Asia and the stories to explain their introduction are every bit as colourful as their plumage. The most enduring legend is that they flew off the set of The African Queen during filming of the 1951 movie at Isleworth studios. Others point the finger at Jimi Hendrix for releasing a pair on Carnaby Street at the height of the Swinging Sixties. More probable is that London’s parakeet population – the current estimate is 30,000 and growing – established itself after successive escapes from pet shops and aviaries. Perhaps not as numerous as in other parts of the capital, where parakeets are accused of beating woodpeckers and nuthatches to the choicest nesting sites, the Heath’s contingent has been around for decades and seems to coexist happily with the locals. Then there were the grey squirrels. Victorians were the first to take a shine to the bushy-tailed rodents from North America and did their darnedest to spread them around the countryside. Woodland managers and red squirrel lovers alike have been gnashing their teeth ever since.

There’s not much natural about the landscape either. Like every other part of Britain, Hampstead Heath has been managed and manipulated by people for centuries if not millennia. Cattle, sheep and goats – all first domesticated in the Middle East – have been raised here since the Neolithic period, suppressing forest regrowth and creating pasture. These days grazing duties fall to rabbits introduced from the Iberian Peninsula by the Normans. Or was it the Romans? Rabbits would give squirrels a run for their money for the title of ‘world’s worst pest’ – just ask an Aussie farmer – but on the Heath they get a pass because their incessant munching helps preserve the acid grassland, and in turn a community of rare heathland organisms. From the eighteenth century, what little was left of the Heath’s primeval woodland of pedunculate and sessile oaks, beech and birch – long exploited for timber and fuel – began to be ‘enhanced’ with Turkey oaks, horse-chestnuts, black locusts, rhododendrons, laurels and dozens more species from around the world. Early plantings were at the behest of aristocrats like Sir Thomas Maryon Wilson, Lord of Hampstead Manor, and the Mansfields of Kenwood House, whose estates constituted or bordered the Heath, but the ‘parkifying’, which included planting still more exotic trees and shrubs, continued long after the 1871 Act.

Meanwhile, the Heath’s mineral-rich springs, dribbling out where porous Bagshot Sands meet impermeable London Clay, were exploited for drinking, laundry and their therapeutic properties. In time, the water, which had once collected in mosquito-infested swamps and bogs, was corralled into a series of ponds, which would later become a playground for bathers and anglers. Here, too, the roll-call of introductions is impressive from mandarin ducks and Canada geese to alpine newts and marsh frogs, from carp and catfish to red-eared terrapins. Some got here under their own steam. Most received a helping hand.

Human agency is suspected in particular for the arrival of two types of crayfish, among the Heath’s more infamous aquatic denizens. The Turkish, or narrow-clawed, crayfish reached Britain in the 1930s, being joined in the 1990s by the red swamp crayfish from North America. Culinary motives are thought to have driven both introductions, with persons unknown considering Hampstead Heath the ideal place to rear them. They were spot on, for the two crayfish varieties multiplied, and are today well-entrenched in the ponds. This became painfully evident in 2012 when swimmers in the men’s pond complained of being nipped on the toes and, according to one report, ‘in altogether more sensitive places’. It gives ‘bottom-feeder’ a whole new meaning. Not long ago, the City of London Corporation, who manage the Heath, removed 500 red swamp crayfish from a single pond during routine maintenance over the course of just three days. With a single female producing up to 600 viable young in one go, total eradication is a tall order.

The point is that Hampstead Heath is populated by lots of living things from other parts of the world, many of them breeding and difficult to control. And I haven’t yet mentioned some of the more notorious: plants such as Himalayan balsam, Japanese knotweed and giant hogweed; insect pests like oak processionary moth and harlequin ladybird; and virulent pathogens, such as Dutch elm disease, ash dieback and Massaria disease, which attacks plane trees. But, in this respect, Hampstead Heath is nothing special. I could have gone to pretty much any park in London, or indeed anywhere in Britain, and seen the same things, and far more besides. And it’s not just parks: our rivers, lakes and streams; our forests and farmland; our estuaries and coastal waters; our homes and gardens; even our own bodies; all host a wealth of introduced species.

Many Brits pride themselves as stoic defenders of a green and pleasant land, boasting a record of resistance against aggressors dating back centuries, be it weathering the Spanish Armada or defying Hitler’s Blitzkrieg. This patriotic fervour, and its clarion call ‘to control borders’, may in part explain the 2016 Brexit vote. Yet, a cursory examination of the natural world reveals that while many interlopers of the human variety have been kept at bay, our islands have throughout history been colonised by a succession of animals, plants, fungi and other organisms that apparently belong elsewhere. Indeed, it’s often hard to sort out the native from foreign.

Philosophers and scientists have long noted the spread and impacts of introduced animals and plants around the world. In his Naturalis Historia, published around 78 CE, Pliny the Elder wrote of Spanish rabbits, whose ‘fertility is beyond counting’, bringing such famine to the Balearic islands by ravaging the crops that the inhabitants begged the Emperor Augustus for military aid. Charles Darwin likewise observed the rampant spread of a European thistle across several South American islands during his nineteenth-century voyage on the Beagle. And, closer to home, in 1920 the Scottish writer James Ritchie highlighted the challenge to ‘Nature’s order’ posed by ‘many thoughtless introductions’, arguing that ‘the alien stowaways which become established in a country include more economic pests than the native fauna they invade’. Yet, until the 1958 publication of The Ecology of Invasions by Animals and Plants, the march of non-native species was largely invisible to the wider public.

Its author, the pioneering British ecologist Charles Elton, believed that we faced a decisive battle whose outcome would determine the fate of the world. The book was an expansion of his series of BBC radio lectures entitled ‘Balance and Barrier’ and opened with a warning of the existential threat presented not only by nuclear bombs – the Cold War was by then gearing up – but by ‘ecological explosions’. Elton defined these as ‘the enormous increase in numbers of some kind of living organism – it may be an infectious virus like influenza, or a bacterium like bubonic plague, or a fungus like that of the potato disease, a green plant like the prickly pear, or an animal like the grey squirrel’. He identified ‘the movement around the world by man of plants, especially those intentionally brought for crops or garden ornament or forestry’ as among the primary reasons for the spread and establishment of new organisms. ‘Just as trade followed the flag,’ added Elton, ‘so animals have followed the plants.’

In the decades since, international commerce has continued to grow and the ecological explosions have kept on detonating. In 2016 – the year Asian hornets were discovered in Britain for the first time, sparking a military-style response to make Elton proud – the first specimen of the Obama flatworm slithered into Britain. Native to South America, the species reaches seven centimetres in length and devours earthworms and other important soil invertebrates. This one turned up in an Oxfordshire garden centre courtesy of a pot plant from the Netherlands. The flatworm wasn’t christened in honour of the former American President but instead derives its name from the Brazilian Tupi for ‘leaf animal’. That same year, three new infestations of the ‘Asian super ant’ were discovered. Hailing from Turkey and Uzbekistan, this social insect forms supercolonies numbering in the millions and is also nicknamed the ‘electricity ant’ for its inclination to congregate in power sockets and light switches, chewing cables and threatening black-outs. Recent years have also seen harlequin ladybirds from Asia kill off our home-grown varieties; Pacific sea squirts carpet our marinas; and buddleia and Japanese knotweed move down the rail network more efficiently than most trains.

Public awareness of the issue is higher than ever before, with sensational news headlines stoking our fears. Giant hogweed, introduced as a horticultural curiosity from the Caucasus mountains in the 1820s, has been recast as Britain’s ‘most dangerous plant’ with sap that ‘melts’ a child’s skin. ‘Monster goldfish’ are on the prowl. ‘Sex mad Spanish slugs’ are terrorising our gardens. Emotive terminology isn’t just the preserve of tabloids: even serious scientists will talk about ‘demon shrimps’ and ‘killer algae’ with a straight face. Some of the language has a xenophobic flavour: introduced plants and animals are ‘ex-pats’ or ‘immigrants’, which ‘pollute’ our pristine environment and need to be ‘bashed’ and ‘sent home’. Perhaps it’s telling that the Nazis were among the first to take against non-natives, drafting a ‘Reich Landscape Law’ in 1941 banishing exotic plants from pure German landscapes. Some argue that the current fixation with non-indigenous wildlife is bound up with subliminal, and not so subliminal, antipathy to arrivals of the human kind. Concerns about non-natives and immigration to our small, overcrowded island are, they say, all of a piece. Even the term ‘invasive species’ has its drawbacks, perpetuating Elton’s notion that we are somehow under assault, as if rhododendrons, grey squirrels and Asian hornets were working to a strict battle plan. The word ‘alien’, which remains in wide use, particularly among botanists, can have similarly unfortunate connotations. Worries about many non-natives can be whipped up unnecessarily, and sometimes for unsavoury political ends. But we shouldn’t avoid talking about them: new organisms are arriving all the time, the pace of arrivals is rising and, yes, a handful of them do appear to cause problems.

There are other issues to consider. An invasive species is commonly thought of as a non-native organism whose population is increasing and spreading, and which causes, or may in the future cause, negative environmental, economic or social impacts. But what do we mean by ‘non-native’? The usual understanding is that it’s an organism introduced into a new country by people – on purpose or by accident – rather than getting there ‘naturally’ by walking, flying, swimming or wafting on the wind. In Britain, this often means anything brought here after rising sea levels cut us off from the European continent sometime between 7,000 and 9,500 years ago at the end of the last Ice Age. But what then do we call extinct fauna and flora that we have since reintroduced? The western capercaillie and European beaver, both around long before we became an island, were wiped out less than 300 years ago by hunting. According to the above interpretation, we couldn’t treat them as ‘non-native’, yet both occur in twenty-first-century Britain thanks to human intervention. (The capercaillie was reintroduced to Scotland in the late 1830s, and successful releases of beaver have occurred at several locations across the UK over the last decade or so.)

At least with our current population of capercaillies and beavers we are sure how and why they’re here. But, with many other species, it can be tricky to know when they first arrived, and whether people were involved. The sycamore, first recorded growing in the wild in Britain in 1632, is often regarded as introduced. Some say it was brought over in the fifteenth or sixteenth century, others suggest an earlier, possibly Roman, introduction, but either way we’re looking at a non-native. Or are we? The problem is that sycamores, indigenous to central Europe, are fast-growing, fast-spreading trees well suited to Britain’s temperate climate. While people have planted most of our sycamore stands, we can’t exclude the possibility that sycamore seeds may have also taken root naturally from time to time having been blown across from the continent. If true, our sycamore population might comprise both natives and non-natives.

A question mark also hangs over the white-clawed crayfish. Considered our sole indigenous freshwater crayfish, and the focus of intensive conservation activity, some experts now suspect the crustacean was introduced for food in the thirteenth century. Even with things that we’re 100 per cent sure are foreign, pinning how and when they arrived is a challenge.

Advances in DNA sequencing and analysis techniques are now shedding light on these mysteries. For instance, the presence on the Orkney Islands, off the north coast of Scotland, of a vole found nowhere else in Britain is something of a conundrum. The Orkney vole, as it’s known, is an endemic subspecies of the common vole, a variety found on the European continent. So, did the Orkney vole scamper there naturally on a temporary land bridge from Europe before the last Ice Age, 20,000 years ago, and somehow manage to weather the chill while its British mainland relatives died out? Or, as seems more probable and has long been suspected, is the vole a far more recent introduction by people? Genetic studies seem to support the latter hypothesis, with Orkney voles shown to be more related to those in southwest France and Spain than to geographically closer populations. The voles are now thought to have arrived with humans on Orkney during the Neolithic period some 5,000 years ago in ships directly from the continent. The rodents may have stowed away in consignments of livestock fodder, or were intentionally brought as food items, pets or even for religious reasons.

Another difficulty with the notion of an invasive species as currently defined are those organisms, unarguably native, which behave in a manner that can only be described as, well, ‘invasive’. Take hedgehogs. On the British mainland they couldn’t be more popular; and faced by a catalogue of threats including habitat loss and agricultural pesticides, not to mention the risk of being flattened by motor vehicles, they’re the focus of a nationwide preservation society. Yet on islands, Mrs Tiggy-Winkle goes berserk.

In 1974, someone on South Uist in Scotland’s Outer Hebrides released half a dozen hedgehogs into their garden to keep down the slugs and snails. Within a couple of decades, the introduced mammal’s population had swollen to 5,000 individuals, and had spread across causeways to the nearby islands of Benbecula and North Uist. The Hebridean hedgehogs eschewed garden pests in favour of the chicks and eggs of dunlins, ringed plovers, redshanks, lapwings and other shoreline birds, and are implicated in a 50 per cent decline in their numbers. Since 2001, nearly £3 million has been spent on removing the invaders. At first, they were culled with lethal injection, but tactics changed when animal rights groups kicked up a stink, so right now the hedgehogs are trapped alive and released on the mainland. In New Zealand, where introduced European hedgehogs have also run riot, the authorities have been less squeamish, eradicating them from the 86-hectare Quail Island.

Natives don’t just act up on islands. Foxes and carrion crows, both indigenous to the UK, can obliterate nesting bird colonies. Red and roe deer can be every bit as destructive to woodlands and agricultural crops as their introduced counterparts: muntjac, fallow and sika deer. Common ragwort, bracken, brambles and nettles – natives all – often spread out of control, suppressing other plants, and are sometimes regarded as weeds. Even beech trees, indigenous to England, upset Scottish conservationists when their seedlings throw shade north of the border. A further complication is that a non-native might misbehave in one location but elsewhere – typically back home – cause no trouble at all, indeed may even be endangered. So, it’s seldom fair to tar the entire species with the invasive brush. The hedgehog was one example but there are plenty more, such as the rhododendron, which spreads aggressively here but not in New Zealand, or the Japanese knotweed, whose penetrating roots are blamed for weakening buildings across Europe but which in Asia is surprisingly scarce.

Professor Helen Roy, a leading British expert on biological invasions based at the Centre for Ecology and Hydrology in Oxfordshire, suggests that perhaps the only time when an understanding of whether a troublesome organism is native or not truly matters is when an incursion is still recent, or hasn’t yet occurred, since it offers a possibility of intercepting it. Most of the time, though, the focus might be better spent on understanding, managing and, where practical, reducing any negative impacts of the troublemaker in question.

Despite these complexities, the term ‘invasive species’, as a label for fast-spreading, harmful non-native organisms, seems embedded in the common psyche. So how many do we have now in Britain? This is difficult to answer but thinking about it in terms of the invasion process can help. Scientists recognise several key hurdles any aspiring invader must clear. First, the organism needs an ‘invasion pathway’; in other words it must get itself transported to a new region by humans. We may intentionally facilitate this, as with organisms brought for agriculture, hunting, horticulture, aquaculture, as biological control agents and for countless other reasons. But plenty of things use us to move around without our consent; think of plankton suspended in the ballast water of ocean-going vessels, the legions of wood-boring beetles holed up in internationally traded furniture, the seeds and spores peppering the mud of a tourist’s hiking boots, the soil-borne invertebrates hitching a ride in plant pots. Crucially, the globetrotter must survive transit. This is no mean feat; the journey might take weeks during which the stowaway may be subjected to extremes of temperature, lack of food or moisture, and other privations. And that’s even before the prospective invader has to contend with strict quarantine measures imposed by vigilant customs officials.

Before moving on, an important clarification is perhaps required. Should a new species reach our shores from its region of origin with no direct human intervention – be it by flying, rafting on an ocean current, blowing in the wind, catching a ride on a (non-human) animal, or in some other fashion – then this organism is classed as a ‘natural colonist’, and not counted in the statistics. A classic example would be the Eurasian collared dove, which started spreading west from Asia in the nineteenth century and was first recorded breeding in Norfolk in 1955. The distinction between natural colonist and human-mediated invader is not always as clear-cut. For instance, how to treat all those weird and wonderful new species set to colonise Britain – both on land and off our coasts – as the climate begins to warm? We may not directly be involved in their spread, but since human activities are driving global climate change, we are not innocent of this process. We might be happy to welcome recent natural colonists such as the tree bumblebee and small red-eyed damselfly, but are liable to baulk at accepting a malarial mosquito.

Importantly, though, an element of the natural about part of a new organism’s journey movement won’t earn it a pass as a natural colonist, if humans are known to have played a key role somewhere along the line. Take the Asian hornet and harlequin ladybird. Both insects are thought to have made incursions from the continent as a result of individuals blowing across the English Channel, but both only reached Europe in the first place as a result of human activities: the shipping of pottery from China, in the case of the hornet, and introduction as an agent of biological control, in the case of the ladybird.

On arrival, the introduced organism then has to escape and reproduce. Those that maintain a viable population, without further human intervention, are regarded as ‘established’ or ‘naturalised’, the rest dismissed as ‘casuals’. (Incidentally, the term ‘feral’, according to Sir Christopher Lever, a British author of several well-known books on introduced animals, should be reserved for creatures that have ‘lapsed into the wild from a domesticated condition’, not simply escaped from captivity. Noting that populations of the American mink established in the British countryside are often referred to as ‘feral’, Lever insists that to regard the non-native mammal as ‘domesticated’ is ‘preposterous and wrong’.)

Only around 10 per cent of organisms brought to a new country persist unaided in the wild. Disagreements over what constitutes non-native flora and fauna, along with the patchiness of data, have led to varying estimates of the number in Britain. The most recent figures, for 2017, suggest that 3,163 species were present in England, Scotland and Wales, of which 1,980 – mostly plants – had established and were reproducing in the wild. In Ireland, there are at least 1,266 non-native species, of which two-thirds are plants.

Finally, for something to be regarded as truly invasive, it needs to spread and expand its population enough to cause measurable negative impacts. On average, a minority of established non-natives register as a problem, although the likelihood of invasiveness varies: just 4 per cent of introduced insects in Britain are classed as invasive, compared with 32 per cent of non-native fish and 85 per cent of exotic plants.

This is all a long-winded way of saying that a tiny proportion of introduced species will ever earn the title ‘invasive’. According to Helen Roy’s team, which keeps a running score, in 2017 at least 275 (about 9 per cent) of the non-natives established in England, Scotland and Wales cause negative impacts. While around 5 per cent of the 1,266 introduced species recorded in Ireland are classed as invasive. These numbers will almost certainly climb.

So, let’s turn to those impacts which can be classed as environmental, economic or social. Again, there is much debate, but the number one ‘environmental’ charge against invasives is that they harm natives, through predation, competition or, perhaps, by spreading disease. Invasive species are increasingly listed alongside habitat destruction, pollution and overhunting as key threats to wildlife. The 2005 Millennium Ecosystem Assessment says they’re a major driver of biodiversity loss. A recent review of 247 kinds of plants and animals around the world that had vanished since 1500 found invasives to be the second most common cause of extinction (hunting, fishing or harvesting came first). For the amphibians, mammals and reptiles on this list of the disappeared, invasives were the number one culprit. Among the most frequent offenders were rats, cats and goats, along with diseases, such as avian malaria and chytridiomycosis, a fungal condition that is wiping out amphibians around the world.

Many of the most often cited cases of extinctions caused, or at least hastened, by introduced species come from islands. Famous examples include a near-flightless wren wiped out by the lighthouse-keeper’s cat on New Zealand’s Stephen Island; the dozen sorts of birds thought to have been extirpated by the brown tree snakes on Guam in the Pacific; or the eight varieties of endemic rodent dispatched on the Galapagos Islands by ship rats. A well-known non-island case comes from Lake Victoria in East Africa where the Nile perch was released by colonial Brits for sport-fishing in the late 1950s. This fast-growing predator has since been blamed for the loss of two-thirds of the lake’s 300 types of endemic cichlid fish, although the introduction may merely have delivered the coup de grâce to dwindling populations already threatened by decades of over-harvesting and pollution.

Back here in Britain, concrete evidence for extinction is scarce, but we can’t ignore two examples where introductions have threatened other species and could lead to their demise. While grey squirrels don’t directly interfere with native red squirrels, they outcompete them for food, especially in deciduous woodland, and also pass on a lethal virus. The red’s population crashed in the wake of the grey’s arrival, so it’s hard to avoid the conclusion that grey squirrels are a big part of the problem. Disease is also a reason that signal crayfish, brought from North America in the 1970s for aquaculture, are displacing Britain’s white-clawed crayfish (which, as mentioned, may or may not be a true native). In this case, the signals pass on a fungal-like pathogen to the white-claws, which die within weeks of being infected. To be fair, ‘crayfish plague’ was already expunging the white-clawed population before signals came on the scene. Indeed, it was the signal’s resistance to the plague that had recommended the crustacean to fish farmers in the first place.

There’s no doubting, however, that even where an introduced species doesn’t kill off a native, it can contribute to significant population declines. And if the impacts are only felt locally, it’s still a concern. For instance, pirri-pirri burr, an Antipodean plant invader which reached Britain at the beginning of the twentieth century, probably as a hitch-hiker in sheep fleeces, will never trigger a national emergency, but in certain places – notably, Minsmere in Suffolk, and Lindisfarne island off the Northumberland coast – it threatens local wildlife.

Another problem, as some see it, wrought by invasive species is hybridisation. Even if non-natives seldom exterminate our home-grown wildlife, the tendency of many to interbreed with them is beyond the pale. Perhaps the best outcome is when the offspring prove sterile, although this represents, for the native, a waste of valuable breeding effort. More serious are cases where viable progeny arise and in turn back-cross with the indigenous species; this sort of thing can erode the gene pool, reducing the population’s genetic variation and leaving it vulnerable to extinction. Hybridisation between native red deer and smaller introduced sika deer – an Asian variety – in parts of Scotland is a well-known example. Over time as the genes mix, red deer are starting to get smaller and sikas larger. As the two deer approach each other in size, this facilitates further hybridisation and risks accelerating negative impacts. Occasionally, hybridisation results in a more vigorous strain, as seems to be happening with the bluebell. Half the entire global population of this much-loved wildflower is found in this country, but a fertile hybrid has also established here, the result of a cross between the native bluebell and a Spanish variety introduced by horticulturists in the late nineteenth century. Many bluebells in Britain’s gardens and urban areas turn out to be this hybrid, although even experts struggle to tell the difference and, for now at least, the hybrid bluebell does not seem to be invading woodlands. Indeed, recent research suggests that the Spanish bluebell is less fertile, and sets fewer seeds, than its British counterpart.

Ecologists also fear that invasive organisms could alter ecosystems in far more profound ways. These could include anything from changing water quality or soil nutrient levels to disrupting food webs, reducing pollination rates and generally messing about with the ‘balance of nature’. Examples at random from around the world include the Mediterranean tamarisk tree, blamed for drying up marshes and salinising the soil in California, or zebra mussels altering nitrogen and phosphorus levels in freshwater habitats. One school of thought suggests that since ecosystems are dynamic and ever-changing, perhaps we shouldn’t be too bothered. Such an attitude is simplistic and defeatist. Much of what humans – the most ‘invasive’ species of all – have done, from cutting down rainforests to spilling oil into the sea, from landfilling toxic waste to pumping out carbon dioxide, has upset ecosystems, and we need to understand and combat those negative effects however subtle. Right now – not for want of research – our understanding of how ecosystems function, how different organisms interact, and what makes these complex systems more resilient, or less, remains limited, with plenty of knowledge gaps left to fill. We are instinctively concerned each time a species is lost from a natural system through our actions (or negligence); we should also perhaps feel a similar disquiet whenever we cause a new one to be added.

If the invaders left people alone and restricted their impacts to the degrading of natural ecosystems, that would be bad enough – not least as we ultimately depend upon these systems for our survival and wellbeing. But some non-natives harm us directly. Notwithstanding the odd pinch on the privates from a crayfish, the obvious threat is their role as agents of disease. The most notorious example in history is offered by the Black Death, inflicted by a strain of bacteria originating in Asia which, from the fourteenth century onwards, has killed tens of millions across Europe, the Middle East and North Africa. While nothing on that scale has recently been visited upon us here in Britain, new parasites and pathogens are on the radar, many transmitted by mosquitoes and other biting insects. At the moment, it’s a bit chilly for these to get a foothold here, but with climate change all bets are off.

Judging by the growing scientific literature devoted to the economic impacts of biological invaders, these species hurt our pockets too. Much of the cost arises from direct impacts such as insect pests reducing yields from agriculture and forestry, fish stocks wiped out by disease or the erosion caused when signal crayfish or Chinese mitten crabs tunnel into river banks. To the ledger we must add the eye-watering sums spent on preventing, monitoring and eradicating invasives. In excess of £5 million is spent every year in Britain removing Japanese knotweed alone. Various indirect impacts, trickier to calculate but just as real, and many times greater than the direct costs, can also be attributed to invasives. This is a complex area, but it boils down to the loss of valuable ecosystem services like nutrient cycling, pollination or flood prevention.

Overall costs incurred by invasive non-native organisms are estimated to amount to 5 per cent of the global economy. Across Europe, invasives inflict some £9-billion worth of damage every year. In the UK alone, the figure has been put at about £1.7 billion annually. Although these are ballpark estimates, resting on plenty of assumptions and subject to much debate, governments the world over are taking notice as never before. Invasive species are fast becoming public enemy number one. In 2016, the European Union banned 37 of the most problematic plants and animals from being kept or traded without a permit. These include signal crayfish, raccoons and American skunk cabbage. On this side of the Channel, the Great Britain Non-Native Species Secretariat was set up a decade ago and tasked with detecting and containing invaders, as well as helping to predict and prevent future incursions. Tackling troublesome non-natives is complex: the measures taken can be extraordinary and sometimes cause more problems than they solve, even hurting the very ecosystems they’re intended to protect.

An emerging school of thought is suggesting that the threat of invasive species has been exaggerated, that we should stop worrying about non-natives and even welcome them for the benefits they can bring. At the other extreme, a growing band of conservationists is going beyond simple calls for the eradication of non-natives to campaign for the deliberate reintroduction of a menagerie of native British plants and animals which have become extinct at the hands of humans. To its critics, the ‘re-wilding’ movement is pure eco-nostalgia.

For me though, most fascinating of all is that non-native organisms, invasive or otherwise, from rabbits to rhododendrons, mink to muntjac, hold up a mirror to our own species. Yes, the pace of invasion is higher than ever before but problematic non-natives aren’t a modern phenomenon: they’ve been with us from the outset, as unavoidable a corollary of the human way of life as cleared forests and piles of garbage. From the earliest settlement of our islands and first experiments with farming, through the Roman and medieval times, and the age of exploration by Europeans, to the current period of globalised free-for-all, the story of invasive species is the story of our own past, present and future.

2
First Invaders

‘But while men slept, his enemy came and sowed tares among the wheat, and went his way. But when the blade was sprung up, and brought forth fruit, then appeared the tares also.’

King James Bible, Matthew 13:25–26

For a million years a windswept peninsula in a corner of northwest Europe had seen various species of humans coming and going. The arrivals and departures were synchronised to the advance and retreat of continental glaciers, a dance choreographed by climatic change. They barely registered. A cluster of footprints here, a tidy pile of knapped flints there. Overwintering in caves, the people would emerge to gather shellfish from grass-fringed estuaries, pad through woodland in search of berries and nuts or pick at the carcasses left by lions and giant hyenas. The more ambitious, coveting the freshest meat, bone and fur, would rally family and friends in adrenaline-fuelled pursuits of deer, horse or mammoth.

Make no mistake, even the earliest people were unusual. Britain had never welcomed visitors quite like them, and over the aeons these experiments in humanity forged in the evolutionary crucible of an African valley generated ever more sophisticated results: the grunts of the most obtuse of cavemen took on deeper meanings; people fashioned better weapons and perfected their hunting techniques; they got the hang of butchery and learned to tame fire. Humans would turn their new-found skills on each other from time to time. Yet, for a great sweep of history, these pioneers – Homo antecessor, Homo heidelbergensis and maybe others – were but minor players on a stage dominated by rhinoceros and sabre-toothed cat, bison and bear. A low profile was often the best strategy given the monsters with which the land was shared. People were no more masters of their destiny than were grains of pollen in the air. And, every time the cold rushed back in and the fragrance of the dwindling forest was lost once more to the bitterness of endless tundra, so would humans again retire to more hospitable refuges in southern and southeastern Europe, abandoning the briefly colonised outpost to musk ox, wolverine and ice.

In the milder periods, when permafrost meltwaters inundated what would be known as the English Channel, the peninsula became an island. On one such occasion, some 125,000 years ago, humans found themselves shut out of the party altogether: things were warming up once again and a wealth of plant and animal species had spread back into Britain. But by the time people were on the scene, the land bridge from the continent had been claimed by the rising seas. Elephant, hyena, lion, deer, hippopotamus, elk and other animals had the place to themselves, enjoying a halcyon human-free interlude lasting 65,000 years.

Even Homo sapiens, the most successful hominid – in population terms, at least – to arrive in Britain was no great shakes at first. Originating perhaps more than 200,000 years ago, modern humans took their time getting here. Not for millennia would the most substantial exodus from Africa occur, with one wave of migrants moving along the Indian Ocean coastline towards southeast Asia, and eventually Australasia; another meandering north and west across the Middle East and Europe. When, from around 40,000 years ago, small bands of nomads, each with its own distinctive material culture, started to reach our shores, perhaps in seasonal visits, they found they’d been beaten to it.

Homo neanderthalensis had been eking out a living on Britain’s cold treeless steppes for at least the previous 20,000 years hunting, with flint-tipped wooden spears, woolly mammoth, woolly rhinoceros and probably quite woolly bison. The Neanderthals, with their heavy eyebrow ridges, flared nostrils and stocky physiques, were well suited to the hostile conditions. Yet their days were numbered, the British contingent vanishing within a thousand years of the arrival of modern humans. No one knows why.

It’s tempting to equate correlation with causation and accuse Homo sapiens of behaving as the archetypal invasive species, outcompeting and eradicating a vulnerable native with cunning and violence, perhaps passing on some disease for good measure. But the story appears more complicated: the significant amount of Neanderthal DNA in the modern human genome suggests a peaceful, even romantic, coexistence between the two hominids across continental Europe dating back 100,000 years. Could it be that the two varieties of early human preferred to make love not war? In Britain, at least, it seems they had little direct contact, and in any case the argument is academic since dropping temperatures led to the most recent glacial maximum about 22,000 years ago. Any prospect of human existence was snuffed out for another ten millennia. The ice crept forward, smothering everything, wiping the sheet clean. Another fresh start.

The people who returned to a warming Britain from around 15,000 years ago could still be classed as hunter-gatherers, but there was a greater sophistication about them, judging by the plethora of artefacts and art left behind. They were dog-lovers too, grey wolves having been domesticated to mutual advantage, possibly more than once, during or even before this most recent Ice Age. Moving along the Atlantic coast, the humans tracked herds of reindeer, horse, deer and elk north from their southern European refugia. Some perhaps crossed the English Channel in boats, while others may have sauntered through Doggerland, an expanse of terrain today submerged beneath the North Sea.

These people exploited natural resources with unprecedented intelligence: flint-tipped arrows of hazel, fired from bows of elm, felled aurochs (wild ox), red deer and wild boar with accuracy; the slipperiest of fish were trapped in river weirs purpose-built from willow; birds and smaller mammals were noosed and snared; a wider range of plants was collected, stored and cooked than ever before. People were thinking ahead. Fire was used to manage woodland. Freshly burnt clearings, the ash festooned with appetising plant regrowth, could be used to lure hungry game, which was much easier than tracking a deer or boar through dense forest. Nevertheless, impacts on the landscape were minimal. As in previous migrations people travelled light and, save for the plant seeds brought as food or stuck to clothing and bedding, few in the way of new species were conveyed to Britain during this period. Things though were about to change.

Danger. Tree felling in progress. A yellow warning sign greeted us as we approached the kissing gate. I had expected this: Hembury Hillfort’s website requested visitors to ‘observe cordoned off areas with red and white tapes’, and please to ‘not climb on timber stacks’. Thankfully, given my five-year-old daughter’s enthusiasm for outdoors rampaging, neither woodpiles nor tape were in evidence today. The works programme, aimed at reducing root damage to the site’s archaeology, was finished for the season. The tree clearance had a secondary function, to open up the view: that’s what partly drew us here. Hembury didn’t disappoint.

Twenty minutes later saw us picnicking amid bluebells at its southernmost tip. From the 240-metre-high bluff we were offered stupendous views across the Otter river valley towards the coast at Budleigh (the sea itself was lost in haze). The landscape was a hodgepodge of greens, interrupted here and there with the dull copper of a newly ploughed field, a yellow patch of oilseed rape, and the occasional pale minaret of wood smoke. Just visible to the west was Exeter, and beyond the grey eastern tors of Dartmoor from whose direction a brisk wind blew. Birds sang and robber flies buzzed. There was the faint drone of distant air traffic. Above us circled a pair of buzzards.

‘What can you see?’ I asked my daughter.

‘Cows,’ she replied, mouth stuffed with cheese-and-onion crisps.

Today’s miscellany of embankments, trenches, mounds and other vestiges of Hembury’s convoluted history confounds those wishing to understand it. The modern visitor is further disorientated by colossal beech trees which have erupted from the earthworks, clinging on with tentacular moss-covered roots. Yet its secrets are yielding to the archaeologist’s trowel.

Hembury’s strategic location and defensive qualities have long been recognised by those keen to defend themselves and command the region. It’s a real Russian doll of a place: ostentatious double-ditched ramparts dug in the Iron Age, some 3,000 years ago, surround the entire three-hectare monument, which is perched at the edge of the Blackdown Hills in East Devon. Easy access to nearby iron ores and smelting works perhaps justified the investment in time and effort to shift the countless tonnes of earth by hand. Members of the Belgae tribe, from northern France and the Low Countries, subsequently laid claim to Hembury, making their own mark in about 50 BCE with additional defensive ditches and ridges across the centre of the fort. Then, in the middle of the first century CE, the Roman military too added Hembury to its network of forts – apparently taking it without a fight.

More fascinating still was Hembury’s much earlier, Neolithic, incarnation, dating to around 6,000 years ago. This period was the focus of a pioneering series of digs in the early 1930s undertaken by the Devon Archaeological Exploration Society. The work was led by Dorothy M Liddell, a formidable and inspirational personality, and one of an emerging breed of female archaeologists. (A 17-year-old illustrator called Mary Nicol was one of Liddell’s protégés at Hembury. Later, as Mary Douglas Leakey, she would make her own name with palaeontological discoveries in Africa.) Through meticulous excavations, Liddell detected signs of earlier inhabitation at Hembury, including a causewayed (or interrupted) enclosure; post-holes denoting a once-grand timber gateway; the remnants of daub huts; shallow cooking pits, a metre and a half in diameter; and traces of a circular wooden building, possibly a guard house. Her team also recovered flint arrowheads and axes, and other stone implements, along with jet and greyish steatite beads and some of the earliest pieces of southern English pottery. Known as ‘Hembury ware’, the latter included simple round-bottomed bowls with lug handles, made using gabbroic clay, an orange-coloured mineral naturally occurring around the Lizard in Cornwall, 200 kilometres to the west. The finds hinted at a connection to an ancient and extensive commercial network stretching across the region and beyond.

But, for me, Liddell’s most important discovery at Hembury were some charred grains of spelt, an ancient form of wheat. Carbon dated at roughly 5,000 years old, these represent some of the earliest archaeological evidence for the cereal anywhere in Britain. Liddell also turned up stone querns for grinding the crop into flour. Evidence of the importance of cereals in the diet of Hembury’s Neolithic occupants was bolstered by the later discovery of 13 impressions of wheat grains embedded within some of the Neolithic ceramics.

How and why did a food plant native to the Middle East – 3,500 kilometres distant – come to be eaten atop a windy promontory in southwest England? The answer lies much further back in time.

Some 23,000 years ago, while Britain and the rest of northern Europe was gripped in an endless winter, people basking in the more benign climate of the eastern Mediterranean were gathering, grinding and cooking the grains of wild wheat, barley, oats and other grasses. It’s possible that the most far-sighted and patient among them may have planted out some of their seeds and waited to harvest a crop. The evidence for such an innovation back then is patchy, but certainly by around 12,500 years ago farming communities had materialised across the region.

The specifics of the transition from restless nomadism to a sedentary way of life based on cereal cultivation are still to be understood, but the shift is remarkably well documented in the Natufians, a people whose settlements are scattered across what is today Israel, Palestine, Jordan, northern Syria and southeastern Turkey. From about 14,500 years ago they started exploiting wild grasses such as emmer wheat and barley to make flatbread, beer and, later, animal feed. The transition from hunter-gatherer to settled farmer was by no means simple and direct. For some reason, the Natufians, having earlier taken up agriculture based on the intensive harvesting of wild grains, decided to resume a more mobile existence around 12,800 years ago. This about-turn has been linked to a colder period known as the Younger Dryas that reduced the natural availability of wild cereals in the Mediterranean region, forcing people to keep moving to fill their bellies.

Eventually, the Natufians and others returned to the cultivation of cereals. By selecting varieties with the greatest yields, or those which thrived in diverse conditions, crops were gradually domesticated. Early agriculturalists benefited from a common mutation in wild wheat and barley that causes the grain-carrying spikelets to be more tightly gripped to the plant after ripening – just when they should be releasing them. In wild conditions, these ‘non-shattering’ mutants are at a competitive disadvantage compared to normal grasses which can spread their seed far and wide, but they lend themselves to being harvested and cultivated by humans. People learned to exploit other plants too, including flax, pea, chickpea, lentil and bitter vetch, intentionally planting, tending and harvesting them.

Scientists wonder whether the timing of this shift to crop domestication, which probably occurred independently in different places across the Fertile Crescent – as well as in parts of eastern Asia where wild varieties of millet and rice were the grains of choice – might not be a coincidence. One suggestion is that as the climate warmed at the end of the last Ice Age, and sea levels rose, so people were forced to higher ground where they would have encountered wild wheat and barley growing naturally. Levels of carbon dioxide were also increasing in the atmosphere – possibly due to its release from warming oceans – boosting worldwide plant production, including grasses such as cereals, and kick-starting what is often called the Neolithic revolution.

With the right kind of seeds, well-prepared soil and a favourable climate, the pioneer farmers soon found themselves amassing more food than they needed. This calorie boost, combined with a reduction in energy spent moving around, is thought to have ramped up human reproductive rates. A population boom led to civilisations across the Fertile Crescent, an 800-kilometre arc of territory encompassing the floodplains of the Nile, Tigris and Euphrates. But the discovery of farming may have set off a vicious cycle: the more people bred, the more food was needed and the harder everyone had to work. If they didn’t want to, or couldn’t, they might cheat or steal, requiring strong laws and even stronger rulers to keep the peace. Of course, there was nothing stopping rulers themselves from hoarding food and growing their own power in the process. At the same time, more and more of the landscape was turned over to crops which meant an acceleration in deforestation, erosion and other varieties of environmental degradation.

Unsurprisingly, given its peripheral location and challenging climate, Britain wasn’t an early adopter of agriculture. By the time wheat and barley made their appearance here some 6,000 years ago – and those precious spelt grains were being hoarded in a primitive hut on Hembury hill – the world’s first city of Uruk was already rising from the Mesopotamian floodplain. The farming of livestock also appeared in Britain, and the rest of northern Europe, around this time, again having been pioneered long before in the Middle East.

Goats and sheep are believed to have been domesticated from their wild ancestors – bezoar and mouflon, respectively – across southwest Asia from about 11,000 years ago. These low-maintenance creatures, compatible with a semi-nomadic lifestyle, were probably first kept for their flesh alone, and only later used for milk, wool and other secondary products. The fertilising properties of livestock manure was also noticed and exploited. Despite their benefits, sheep and goats would go on to become among the world’s most destructive invaders, especially on islands where their relentless chomping wipes out rare plants and degrades ecosystems. Indeed, their unfussy diet, their rapid reproductive rate, their tolerance of a breadth of environmental conditions – the very traits which first drew us to them and of course to so many other problematic species – go a long way to explaining their world domination. At the last count, two billion sheep and goats roamed the planet.

Around the time that people first domesticated sheep and goats, cattle also joined the ranks of tamed ruminants. Cows were descended from the extinct wild ox, or aurochs. This was a spectacular beast, particularly the bull which stood nearly two metres high at the shoulder and sported fearsomely curved horns. Unlike the bezoar and mouflon, aurochs were already present in post-glacial Britain – indeed, they roamed the entire Eurasian landmass; however, domestication probably occurred in the Middle East. That’s because early cattle were much smaller than our native aurochs, and DNA studies show that modern cows, including British ones, are genetically closer to Syrian aurochs than home-grown ones. In fact, today’s entire global cattle herd – numbering some 1.5 billion cows – is believed to be descended from a founding stock of just 80 animals, likely to have originated in the Middle East. There’s a good chance, however, that hybridisation would have occurred between local British aurochs and the smaller incoming cattle. Neolithic farmers may not have been thrilled about this: their petite cows, bred for milking, may have risked serious injury when attempting to birth an outsized hybrid calf.

Other modern domesticates with native British versions also seem to have derived from imported stock. These include the pig, whose ancestor, the wild boar, was widespread here before the advent of agriculture. Porkers are thought to have been first farmed in the eastern Anatolian region of modern-day Turkey about 10,000 years ago – along with a later independent domestication event in central China – and descendants of these Anatolian versions were subsequently brought to Britain. As with cattle, the amount of wild boar DNA in the genome of domestic pigs suggests frequent hybridisation between the two. To an extent, this may have benefited pig farmers, as crossbred versions may have been better suited to the more bracing local conditions in Britain, although too much of the ‘wild’ in a pig could make it a handful. A balance had to be struck.

Many of our supposedly native crops may also have come from elsewhere too. For instance, Britain’s blackberries, raspberries, carrots and parsnips, as well as the perennial ryegrass, red clover and common vetch traditionally used as animal fodder, all probably derive from southern European strains.

Whether there’s the whiff of the exotic about other domesticated species is less certain. For instance, the honeybee is thought to have originated in Asia, or maybe Africa, around 300,000 years ago, later spreading naturally across Europe, so the likely presence of this woodland insect in Britain before the most recent Ice Age would qualify it as native. Yet, the earliest known archaeological evidence for honeybee exploitation by humans in this country – as suggested by beeswax residues on seven pieces of Neolithic pottery found in southern England – dates to as recently as 4,000 years ago. That’s several millennia after sweet-toothed pioneer farmers in Turkey, and later in central Europe, began gathering honey and wax from the insects, and possibly even domesticating them. So, we’re left to wonder if Britain’s first apiarists collected honey from wild bees or perhaps were using a tamer, introduced, variety that had been bred on the continent. In a sense, this discussion is somewhat academic, since pretty much all of our honeybees are today derived from southern European stock after parasitic mites devastated Britain’s existing honeybee population in the early twentieth century.

So, how did the ‘Neolithic package’ – although this term for an apparent commonality of elements, including domesticated crops and livestock, along with other characteristic artefacts, is increasingly criticised as over-simplistic – reach our shores? Did Fertile Crescent farmers themselves migrate north and west, or was it just their agricultural practices that travelled, along with the wheat, barley, sheep, goats and other domesticated species upon which they were reliant? The question has been debated for well over a century, although recent research is beginning to support the former hypothesis. For instance, a genetic study published in 2018 found strong affinities between Mesolithic British and western European hunter-gatherers over a period spanning Britain’s separation from the continent. The authors of this paper believe that British Neolithic people derived much of their ancestry from Anatolian farmers who followed the Mediterranean route of dispersal and entered Britain from northwestern mainland Europe. One thing is certain: when times were good, farming guaranteed a steady food supply and supported a burgeoning human population. In Britain, its practitioners rubbed along with nomadic hunter-gatherers for hundreds if not thousands of years, but the agricultural way of life, and the settled civilisation it supported, proved irresistible. So too, would the invasive species that profited from both.

The omens were there from the start. For millions of years, a spectrum of fast-growing, fast-spreading pioneer plants, both annuals and perennials, evolved to benefit from landscape impacts very similar to those that humans would one day cause. Many were adept at exploiting forest clearings opened up by fallen trees or recolonising habitats scraped clean by fires, glaciers, floods, landslips, volcanic activity and other natural disturbances. So, when the first farmers razed woodland and stripped soil bare in readiness for crops, they were teeing things up for a plethora of undesirable species. Commonly known as ‘weeds’, they have plagued us ever since.

Most troublesome of all were the weeds that resembled crops. These included darnel, a toxic grass which happened to be a dead ringer for wheat, and which infested the Middle East’s earliest agricultural sites. Pastoralism only worsened the situation, as grazing and browsing livestock suppressed tree regrowth, maintaining the sort of open conditions favoured by weeds. What’s more, just like crops, many weeds were adapted to thrive on the elevated levels of soil fertility resulting from all that extra animal dung.

British farmers, like their continental antecedents, set about annihilating the wildwood with their crops and livestock. Shifting agriculture was probably practised at first, with the felling of a few trees and controlled burning of understorey, followed by successive plantings of cereals. After a few seasons, the plot’s soil nutrients were exhausted, forcing people to move on and repeat the destructive pattern. Anthropogenic deforestation was hardly a new thing – as we’ve seen, hunter-gatherers were keen on woodland openings – but its scale from the Neolithic onwards was unparalleled.

Trees were removed for reasons beyond the need for cropland: their timber was a source of both fuel and building material, while the clearances themselves may have held a symbolic value. Britain’s vanishing woodland is reflected in changes in the incidence of particular pollen species in the archaeological record. As the representation of oak, elm, lime and ash dwindled, grasses, shrubs and wildflowers came to the fore. Invertebrate communities also changed, with a decline in specialist forest insects, including those associated with old or decaying timber, their place taken by varieties adapted to open and disturbed ground; dung beetles flourished thanks to livestock. Every so often a prolonged spell of climatic deterioration – as occurred between 5,000 and 3,500 years ago – would lead to a temporary abandonment of arable farming in Britain. Forests then had a chance to recover, although pastoral farming would still have been practised.

Of course, Britain’s Neolithic farmers had their work cut out dealing with the weeds that prospered in the denuded landscape. Many unwanted plants already lurked as seeds in our soil, just waiting for their moment in the sun; others were conveyed from further afield as contaminants of grain imports. The field, or corn, poppy, well-known to early Middle Eastern civilisations, is among the more familiar of the non-natives to have debuted in Britain around this time. The ancient Egyptians were taken by the striking blood-red blooms which infested their wheat and barley fields at harvest. The poppy’s reappearance each year was a metaphor for rebirth and regeneration. The flower was woven into funerary bouquets and depicted on tombs.

Another arrival in Britain was charlock, or wild mustard, which was once described as the most troublesome annual weed of arable land. Indeed, an assortment of familiar crops including artichokes, flax, garden peas, leeks, lentils, lettuces and radishes may have started out as invaders of arable fields. Given that these are all fast-growing, short-lived species thriving on bare soil, their weedy heritage seems to fit. Even einkorn – one of the first types of wheat to be cultivated on a large scale – may have started life as a contaminant of emmer wheat crops. Furthermore, bread wheat, today’s single most important variety, thanks to its easier threshing and greater grain yield, arose in the Fertile Crescent at least 8,500 years ago as a result of hybridisation between emmer and another weed, wild goat grass.

From a British perspective, some of the most important of the arable weeds were rye and wild-oats. Although originating in the Middle East, both seemed better adapted to our miserable climate and harsh soils, and often outperformed wheat and barley. So tenacious were these grassy invaders that by the Early Bronze Age, about 4,000 years ago, central and northern European farmers stopped bothering to weed them out and instead harvested them as crops in their own right. Domesticated varieties of both rye and oats were soon cultivated for bread-making, for flavouring alcoholic drinks, and as animal feed. Wilder versions of the oat stuck around and remain intractable arable weeds to this day, in large part due to the similarities in appearance and lifecycle with those of crops. Selective herbicides are available but hand-weeding, or ‘rogueing’, of wild-oats is still practised on a small scale.

When Brits took to agriculture 6,000 years ago, the door wasn’t just opened to invasive plants. Also waved through was an assortment of animal species adapted to living among people and exploiting their way of life. The house sparrow is a case in point. Remains of this small, gregarious bird have been identified in 10,000-year-old Natufian sites, suggesting sparrows long ago learned to nest in or close to buildings, purloining stored cereals and picking through the rubbish piles. By the Late Bronze Age, about 800 BCE, sparrows are known to have been present in central Sweden, so had probably reached Britain by then too. Today, they’re one of the world’s most cosmopolitan birds, outcompeting indigenous avians and proving a serious agricultural pest. In Russia alone, they’ve been accused of consuming a third of the annual grain production. During the 1950s the Chinese leader, Mao Zedong, even declared war on the sparrow, his scientists reckoning that, for every million birds killed, 60,000 extra people could be fed for a year. Chairman Mao’s scheme backfired: the removal of sparrows resulted in plagues of locusts and other insect pests, whose populations the birds had helped suppress, which in turn led to famine. The Chinese government ended up reintroducing sparrows from the Soviet Union.

It seems therefore that house sparrows have a value in agricultural systems and in Britain, at least, we’re fond of them. The sparrow population has been falling of late: during the 1970s there were up to 12 million of them in the UK, but the population is now half that, with the worst declines in England. No one is really sure what’s killing off sparrows. Possible factors include a reduced availability of invertebrate prey, a shortage of nesting sites and increased predation by squirrels, magpies and cats. In cities, high levels of nitrogen dioxide in the air, mainly from car exhausts, also seems to be a factor, with London alone seeing a 60 per cent decline between 1994 and 2004. All this has triggered urgent conservation efforts to save the sparrow.

Such measures won’t be contemplated any time soon for the house mouse, another accomplished non-native invader, which originated up to a million years ago somewhere between the Middle East and northern India. The rodent was first drawn to the organic waste tips of hunter-gatherer settlements in the southern Levant at least 15,000 years ago and its population was primed to explode with the invention of agriculture. Recent evidence shows the house mouse sometimes shared the more mobile of the Natufian sites with a second species, the short-tailed mouse; however when people settled down for any length of time, the house mouse soon elbowed out its wilder cousin. By the Bronze Age, the rodent had scurried into western Europe but took a while to make its mark in Britain: the earliest records date from pre-Roman Iron Age settlements at Gussage All Saints in Dorset and Danebury Hillfort in Hampshire. The mouse seems to have got established after repeated introductions as a ship stowaway; by then Britain was well connected to the continent by the maritime trade and replete with granaries. Danebury alone boasted some 4,500 pits for storing crops, making it a house mouse heaven.

Along with rabbits, rats and grey squirrels, the house mouse shares the accolade of being among the few vertebrates to inflict both economic and social costs on a national scale. In addition to eating and fouling food stores, the rodent harbours a catalogue of unpalatable (and unpronounceable) diseases from tularaemia and typhus to leptospirosis and lymphocytic choriomeningitis. Humans have long waged a losing war against the species. These days baited traps and poisons tend to be used, but in times past barley cakes, spiked with black hellebore (a toxic variety of buttercup), would be placed at the entrance to their holes. Mice were also said to flee a censer of haematite stone and burning green tamarisk. But nature also provided a more elegant solution to the rodent problem.

The African wildcat’s mouse-destroying prowess, along with its skill as a bird and fish catcher, may have been what recommended the species as the perfect household pet to the Egyptians more than 4,000 years ago. If true, that would make its tame version, the domestic cat, an early agent of biological control (the use of one organism to reduce populations of another). The sacred importance of cats in ancient Egypt is the stuff of legend with the feline deity Bastet worshipped as a goddess of fertility and the moon. The Greek historian Herodotus famously – but perhaps not altogether reliably – reported that the death of a cat prompted all those in the household to shave their eyebrows. The pet would then be embalmed. One cemetery unearthed at Beni Hasan in 1888 was said to contain the remains of 80,000 cats. A 20-tonne consignment of the corpses was later exported to Liverpool as fertiliser. One or two of the mummified moggies were saved for posterity by the city’s museum. The human relationship with cats may predate ancient Egypt, with the suggestion that the felines began domesticating themselves during the Early Neolithic period; as sparrows and mice were drawn to Natufian grain stores and spoil heaps over 10,000 years ago, so cats were drawn to the sparrows and mice. A rise in the feline population may have been further sustained on proffered titbits from people, as well as rummaging through our mounting piles of rubbish.

Like the house mouse, the domestic cat first appeared in Britain towards the end of the Neolithic, with signs of the species at Gussage All Saints and Danebury Hillfort – just like those of its famous rodent quarry. Could it be that the cat’s pest control qualities were appreciated in Iron Age Britain? Cats were, however, rare until medieval times. The earliest written record dates to the reign of the Welsh king Howell the Good (880–950 CE), who issued the edict that anyone slaying or stealing a cat was liable for a financial penalty calculated in terms of the equivalent cost in grain: ‘The worth of a cat that is killed or stolen; its head is to be put downwards upon a clean even floor, with its tail lifted upwards, and thus suspended, whilst wheat is poured about it, until the tip of its tail be covered.’ Today, an estimated nine million cats prowl Britain’s towns and countryside, each year snaffling some 100 million prey items, including mammals, birds, reptiles and amphibians. One 1987 study from the village of Felmersham in Bedfordshire implicated cats in almost a third of house sparrow deaths. It seems old habits die hard.

Perhaps the greatest feline felony is a crime of passion. As with cows and pigs, keeping apart wild and domesticated versions often proves futile. The same seems true of pet pussies and Britain’s own native wildcat, an endangered beast confined to the forested margins of Scottish moorland. The two versions have interbred so often that hybrids now dominate the wildcat population. Conservationists worry that too much domestic cat in the genome of the wildcat weakens it and leaves an animal which is already threatened by habitat loss and persecution close to extinction.

The arrival in Britain of a tabby of a different sort is also linked with the advent of Neolithic agriculture. Also known as the grease moth, the large tabby gets its name from the uncanny resemblance that its forewings bear to cat fur. With an appetite for dried dung, dead skin, old feathers, bits of straw and other unmentionable detritus, tabby larvae probably first hitched a ride here ensconced in livestock bedding. Suggesting that its natural habitat might once have been caves, the insect lurks in the gloomy recesses of stables and outhouses, where the larvae spin protective silken tubes about themselves then munch away undisturbed on their rarefied diet for up to two years before turning into adults.

A similar niche is exploited by dermestid beetles, many of whose 1,000 species and subspecies are spread by human migrations and globalised trade. Some are specialist scavengers on desiccated animal remains including hides, furs, feathers, tendons and bone, and a few are associated with Egyptian mummies, as well as with human remains from Middle Bronze Age sites in the southern Levant where the larvae drilled tunnels into the bone. Museum taxidermists still use these insects to nibble flesh from animal skeletons prior to display. Some dermestids could have reached Britain as early as the Neolithic period in the same way as the large tabby moth.

Among a number of non-native insect pests arriving in crop shipments is the grain weevil, a flightless species measuring around four millimetres when full-grown. Mated females each produce 150 eggs or more, which are deposited individually into grain kernels. The developing larvae feed there for up to six months before pupation, after which the adults chew their way out of the now-empty seed hulls. There’s a theory that before agriculture came along the grain weevil’s Asian ancestors lived on food scraps in bird or rodents’ nests, before dispensing with wings altogether and becoming wholly dependent on human food stores. If true, this was a good move, as today the weevil plagues food stores worldwide, gorging on wheat, barley, rye, oats, corn, rice and millet, as well as a range of processed goodies from chocolate to pasta. The earliest western European record is from Early Neolithic Germany up to 7,000 years ago, and the insect is confirmed in Britain from the first century CE. Today, the UK alone spends an estimated £6.5 million annually on pesticides to control these and other non-native invertebrate pests of stored grains and fodder crops, including the saw-toothed grain beetle, foreign grain beetle and the red flour beetle, as well as mites and moths.

The unparalleled growth in human population and radical change in lifestyle unleashed by the Neolithic revolution benefited a different class of invading organisms; organisms that made their livelihoods not just among us, but on and even inside us. Harmful bacteria, viruses, protozoa, fungi, intestinal worms, ticks, lice and fleas, and myriad other nasties had always been present in the environment. For example, the bacteria responsible for tuberculosis, which still kills around three million people annually, was probably infecting the very earliest hominids in East Africa millions of years ago. The guts of hunter-gatherers are thought to have been crawling with roundworm, hookworm and other helminth worms, and their wounds quickly got infested with staphylococcal bacteria. In addition, a miscellany of animal-borne diseases may have infected humans before the Neolithic, from sleeping sickness and schistosomiasis to monkey malaria. But as soon as we started to form dense, semi-permanent, settlements, living side by side with livestock, and inadvertently drinking water contaminated by our own waste (never a good idea), harmful parasites and pathogens of all shapes and sizes were allowed to reach epidemic proportions for the first time.

For instance, the measles virus, in order to persist and spread, requires a sedentary population of up to half a million people with a continually replenishing supply of previously uninfected children. Malaria, yellow fever, diphtheria, leprosy, smallpox, influenza and the common cold are among a wide range of other ‘civilisation diseases’ thought to have benefited from our change of habits, many hopping from domesticated animal to human during, or after, the Neolithic. (The species-jumping may have gone both ways, with evidence that humans could have passed on harmful worms as well as certain other parasites and pathogens to their livestock, rather than vice-versa.) Furthermore, as we have seen, agriculture boosted populations of rodents, birds, invertebrates and other agents of disease. Even without close-living humans, grain stores, and herds of livestock, disturbance to the environment wrought by farming itself probably facilitated the spread of parasites and pathogens. For example, the deforested habitat resulting from slash-and-burn agriculture continues to favour malaria-carrying mosquitoes.

Britain’s remote location, temperate conditions and relatively late adoption of modern farming may have helped its people avoid early epidemics. However, disease outbreaks probably became a fact of life by the Bronze Age with the increase in trade with the continent. Indeed, a catastrophic epidemic could explain the extraordinary results of a recent study on ancient human DNA across Europe which indicates that at least 90 per cent of the ancestry of Britons can be traced to the Beaker people. Named for their characteristic bell-shaped pots, this group originated in central and eastern Europe and arrived in Britain some 4,500 years ago, seemingly replacing almost the entire indigenous population. One suggestion is that the pre-Beaker Brits might have succumbed to a disease to which the Beakers were resistant.

Not everything that arrived towards the end of the Bronze Age and into the Iron Age was quite so unwelcome. By around 2,500 years ago, trade routes were beginning to extend to the Far East, courtesy of new imperial roads built by the Persians, facilitating a westward spread of previously unknown plants and animals. During this period, Brits may have got their first taste of a domestic apple, a species originating in the mountains of Central Asia, or ridden their first donkey, derived from wild asses in Egypt.

The woad plant, a member of the cabbage family prized as a source of indigo dye, was another Asian native appearing in Britain around this time. (Extracting the pigment was a complex process, involving huge quantities of leaves, a fair amount of an alkaline substance, such as lime – made by heating up chalk or limestone in a kiln – or stale urine, and a prolonged fermentation phase.) In De Bello Gallico, Julius Caesar’s account of his seven-year campaign in the first century BCE to subdue the Gauls (another name for the Celts), he records that British warriors dyed themselves with woad to terrify their enemies. This was the inspiration for a blue-faced Mel Gibson in Braveheart. Like many of the best stories it has its doubters: the term Caesar used for ‘woad’ was vitrum, which also translates as ‘glass’, prompting some to suggest that Celts were in fact scarring or tattooing themselves. Whatever the truth, pod fragments and seeds of woad have been discovered in the Late Iron Age site of Dragonby, near Scunthorpe in Lincolnshire, and it’s believed the species was brought by Celts, via western and southern Europe.

The Romans may not have had a hand in bringing this particular plant to Britain, but that’s more than can be said for a whole new wave of non-natives about to make their presence felt. Once again, momentous changes were afoot in this corner of northwestern Europe.

3
Romans and Normans

‘This England never did, nor never shall,

Lie at the proud foot of a conqueror.’

The Life and Death of King John, William Shakespeare, 1623

They didn’t come for the weather, that was for sure. As Aulus Plautius knew only too well, gales, incessant rain and a fleet-destroying storm had scuppered Julius Caesar’s attempts to conquer the island in 55 and 54 BCE. But now, with orders from the new and already beleaguered emperor Claudius ringing in his ears, the general had no choice but to try again. So, when the first Roman caliga squelched into British mud somewhere along the southeast coast in 43 CE, there was a new determination to get the job done and, with 40,000 legionaries, auxiliaries and cavalry troops at his disposal, Plautius could hardly fail. Yes, some opposition would need to be dealt with. Caractacus, chieftain of the Catuvellauni people, was routed at the battle of Medway and his stronghold at Camulodunum – present-day Colchester – seized, but he fled to the west to fight a prolonged insurgency before his eventual capture. A few years later Boudica, the Iceni queen, also had a pop at the invaders, razing Camulodunum, along with Londinium (London) and Verulamium (St Albans). But she, too, succumbed. Rome would never conquer the entire island; however, within a century much had been brought to heel, with the Scots and other recalcitrants left to their own devices.

What Britannia lacked in climate and hospitable welcome was more than offset in mineral wealth: iron in Kent, silver in the Mendips and a generous seam of limestone from Oxfordshire to Lincolnshire, perfect for building roads and towns, aqueducts and bath-houses. Productive agricultural land was widespread too, although scant forest remained. Nevertheless, like all colonists, the Romans felt their new possession wasn’t quite up to scratch.

The food in particular left much to be desired. Little in the way of fruit and veg was grown in Late Iron Age Britain. Notwithstanding the odd amphora of wine, olives, shellfish and other rarefied menu items that some pre-Roman elites are known to have imported, the locals had to content themselves with a diet heavy in oats and barley. A modest range of vegetables was cultivated, but dairy products were seasonal treats and meat a luxury. Most of today’s familiar herbs and spices were absent. For the Romans, this just wouldn’t do. Oats and barley were all very well for the subjugated – or as livestock fodder – but their own tastes were more refined.

The occupying power set about expanding the cuisine, introducing at least 50 new species of plant foods, most originating in the Mediterranean Basin. These included fruits such as peach, pear, fig, mulberry, sour cherry, plum, damson, date and pomegranate, along with almond, pine nut, sweet chestnut and walnut. Romans brought vegetables too, from cultivated leek and lettuce, to cucumber, rape and possibly turnip, along with new varieties of cabbage, carrot, parsnip and asparagus which already grew wild in Britain. Black pepper, coriander, dill, parsley, anise and black cumin added to a bonanza of outlandish flavours. Oil-rich seeds of sesame, hemp and black mustard were also among the arrivals.

Many introductions had supposed medicinal functions too. For the Roman historian, Cato the Elder, the cabbage surpassed all vegetables in that respect. Writing in about 160 BCE, he noted that it ‘promotes digestion marvellously and is an excellent laxative’. Moreover, he insisted, there was nothing better than a warm splash of urine collected from a habitual cabbage-eater to treat headaches, poor eyesight, diseased private parts and sickly newborns. Another plant introduced to Britain for its therapeutic properties was Alexanders – the ‘parsley of Alexandria’ – a chunky lime-green relative of celery, which grew to 150 centimetres in height and was prized as aromatic vegetable and versatile tonic alike. The Romans may have been on to something here: recent chemical analysis of Alexanders reveals high concentrations of the anticancer compound isofuranodiene.

How many of these species were grown in Britain during the occupation rather than imported as ready-to-eat crops is unclear. The sweet chestnut, for instance, a staple of many a legionary’s mess-tin, is absent from the medieval pollen record, suggesting it was grown here only much later. A period of hotter summers across northern Europe, including Britain, during the early years of Roman occupation may have favoured the growth of warmth-loving figs, mulberries, grapes, olives, pine nuts and lentils, albeit on a modest scale, perhaps in garden pots. By the time the Romans left, several introductions, including walnut, carrot and cherry, are known to have fully established themselves.

The origins of certain plants can be traced to Britain’s first formal gardens, laid out during the Roman period. The best-known example is Fishbourne Palace in West Sussex, built in about 75 CE, whose outdoor space boasted tree-shaded colonnades and ornamental water features, along with geometric beds, fertilised with manure and bordered by a decorative hedging box. Fishbourne is now believed to have been the residence of a loyal Brit: Tiberius Claudius Cogidubnus, chieftain of the Regni tribe; if true, it was a handsome reward indeed for his allegiance to the occupying power.

A minority of Roman plant introductions are today regarded as invasive. One of them is probably ground-elder. This iron-rich perennial was cultivated both as culinary herb and for treating arthritis (another name for it is ‘gout weed’), but once its spaghetti-like rhizomes got a foothold, ground-elder was near unstoppable. (Rhizomes are specialised subterranean stem sections capable of putting out both roots and new shoots.) To this day, up to £1 million is spent every year eradicating it from gardens. Some experts say ground-elder is native, but because the weed is usually found close to human habitation its presence here is generally blamed on the Romans.

As we’ve seen, sheep, cattle, pigs and goats were established in Britain prior to 43 CE, but the chicken – today the world’s commonest and most widespread livestock species – was still a rarity in this country, judging from its absence in the archaeological record. This may have been an artefact of the poor preservation of their brittle bones and difficulties in identification. The earliest remains appear in Early Iron Age burial sites (around 800 BCE), in Hertfordshire and Hampshire, and their very scarcity may have perhaps been reason enough to entomb these exotic birds from the Orient with the lately departed. But when, where and why were people first drawn to the red junglefowl, the chicken’s probable wild predecessor? No one knows for sure, but domestication seems to have occurred somewhere in south or southeast Asia around 4,000 years ago, with tame fowl brought to the Mediterranean by the eighth century BCE, reaching central Europe a hundred years later.

Chickens and their eggs have always been eaten, but for much of human history they’ve been as prized for their pugilistic prowess as for their gastronomic qualities. Cockerels, it turned out, need scant encouragement to set at each other with beak, claw and, in the older birds, wickedly sharp leg spurs. The skirmishes have excited the bloodlust of onlookers for generations. Cockfighting spread west across India and the Middle East, the sport in turn captivating the Persians, Greeks and the Romans. Chickens held a religious significance too, the males symbolising the sun god in the Roman cult of Mithras. Caged fowl would be taken on military campaigns and their eating habitats studied for purposes of divination; if your sacred chicken, when offered food, guzzled it down, all augured well for the impending battle. Fowl-keeping in Britain grew in popularity up to and throughout the Roman invasion, albeit the preserve of a privileged few. Here, as elsewhere, chickens were multifunctional, a source of food, entertainment and devotion. Their bones are associated with Roman temples, such as one at Uley in Gloucestershire dedicated to Mercury, and they regularly turn up in Romano-British graves.

Various other animals were imported for nutrition, status and religious reasons, with the remains of pheasant, peafowl, guinea fowl and donkey all found occurring in Roman sites. Elephants were the most impressive creatures brought to Britain; the Emperor Claudius used them to intimidate his new subjects soon after his victory – their stink had the added benefit of panicking enemy horses – although the tuskers’ visit seems to have been fleeting. Archaeologists are intrigued by the discovery at Fishbourne and on the Isle of Thanet, Kent, of numerous bones of fallow deer, a variety hailing from the Anatolia region of modern-day Turkey. Analyses of the deer teeth at both sites indicate well-established, breeding populations, a finding that hints at the existence of what might turn out to be Britain’s earliest deer parks.

As with so many non-natives, the story of fallow deer is far from straightforward since they vanished with the Romans around 400 CE. It was long assumed that the species only returned to Britain with the Normans, but recent radiocarbon dating work suggests they were around just before the Battle of Hastings. Either a few of the Roman deer hung on in the wild, or more likely, small-scale reintroductions, perhaps as novelty items, continued to occur over the course of succeeding centuries.

Sometimes creatures were kept for company alone. That seems to be true both for natives, such as ravens and crows, which were popular pets among the soldiers in Iron Age and Roman Britain, and for the more exotic. Examples of the latter included the Barbary macaque, a monkey whose bones have been recovered from Roman sites at Wroxeter, Dunstable and Catterick.

The Romans weren’t averse to the odd invertebrate too, notably snails, new species of which were introduced as a delicacy. The pot lid, or Burgundy snail remains the most popular of several edible types that now support a multi-million-pound global escargot market. These days snails are largely absent from menus this side of the Channel, where they are regarded as vermin. Indeed, the 5,000 tonnes of molluscicide applied every year to keep them at bay could fill two Olympic swimming pools.

Most creepy-crawlies arriving and spreading during Roman times came unnoticed as hitch-hikers, such as grain weevils. The earliest British remains of these and other insect pests of food stores show up at sites in London and York dating to within the first decades of the Roman occupation, suggesting that infested grain was imported from Europe soon after the invasion. Invertebrate parasites of livestock and people flourished as new forts, towns and cities sprang up, and human population density grew. The Romans were known for their close attention to personal hygiene, with flushable latrines and heated bathwater. Yet, these measures failed to arrest the proliferation of tapeworm, liver flukes, roundworm and whipworm, along with swarms of fleas, lice and the odd bed bug. The widespread prominence of fish tapeworm, a gut parasite attaining nine metres in length, is something of a puzzle since the species is rarely evidenced in earlier, Bronze and Iron Age sites. Here, the Roman weakness for a peculiar condiment called garum may have been the cause. This fermented sauce, a blend of raw freshwater fish and herbs, left to rot in the sun, was traded across the empire and could have helped spread fish tapeworms.

From the late fourth century, the Roman Empire began to wither. Soldiers stationed in Britain were recalled to fight insurgencies on other fronts and by 410 CE the northern outpost had been abandoned. What happened over the next six centuries, traditionally dismissed as the Dark Ages for the paucity of written records, is vague. Roads and other imperial infrastructure disintegrated, vibrant towns and cities decayed, and trade declined, all slowing the influx and spread of new species. Yet, this was a period of great human churn as populations from Ireland, Scotland and other outlying regions of the British Isles moved into undefended territory, joined by continental immigrants, particularly from Scandinavia, the Netherlands and Germany. These movements of Angles, Saxons, Jutes and other peoples would have instigated fresh introductions, deliberate and accidental, but for now the details are lost in time.

The elite are always keen to improve upon what nature has provided and, when it comes to reshaping and enhancing the landscape, few matched the enthusiasm of the Norman invaders of 1066. With a mania for hunting, Britain’s newest overlords depopulated large tracts of territory in the interests of blood sport. Dozens of hunting grounds, or ‘forests’, were designated, encompassing not just wooded areas but moorland, cultivated fields, and even whole villages, from which the occupants were banished under ‘forest law’. Any animals which could jeopardise the chase were also dealt with with ruthless efficiency: sheep and goats, whose grazing could damage the forest vegetation, were removed, and unwanted dogs hobbled in a procedure known as ‘lawing’, which saw the claws from one foot lopped off with mallet and chisel. The Anglo-Saxon Chronicle for 1087 implies that William the Conqueror’s focus was native game: ‘Whoever slew a hart or a hind [male or female red deer] was to be blinded. He forbade the killing of boars even as the killing of harts. He loved the harts as dearly as though he had been their father. Hares, also, he decreed should go free.’ Yet, William and his successors seemed happy to bring in, and protect, foreign quarry species.

This included the fallow deer. Like the indigenous red deer, fallow offered fabulous sport for the mounted hunter and hound by galloping away across the countryside. (The roe, Britain’s other native deer, was far more skittish and a bit of a killjoy: its instinct was to hunker down in thick undergrowth at the least sign of danger, and it could even die of fright.) As discussed, small numbers of fallow deer may already have been present in Britain before the Normans; certainly, by the beginning of the twelfth century the species is known to have been well established. There’s also a possible Sicilian connection here.

After a 30-year campaign, the Normans completed their capture of this Mediterranean island from the Arabs in 1091. Perhaps impressed by the parks of wild animals, including fallow deer, kept by Sicily’s previous rulers, in 1129 King Henry I had 11 kilometres of wall built around his own estate at Woodstock, Oxfordshire, to which he introduced lions, leopards, camels and a porcupine. And fallow deer. According to the archaeologist Naomi Sykes, ‘This collection, which is the direct ancestor of London Zoo, was not simply a frivolity; it was a metaphor for the Norman Empire, a statement that the Norman kings had power not only over the wild creatures in their possession but also over the countries from which the animals derived.’ In addition to being far more manageable than red and roe – their scientific name Dama comes from the Persian for ‘tame’ – fallow thrived on poor quality land, so proved an immediate hit. By the 1300s, the deer had been stocked in some 3,000 parks across Britain; in England alone, these enclosures covered the equivalent of 2 per cent of the entire land area. The modern distribution of fallow deer, whose UK population probably exceeds 200,000 individuals, matches that of the medieval parks from which they escaped. (According to Charles Smith-Jones of the British Deer Society, fallow are remarkably loyal to their home areas and seem inclined to heft strongly to them.) Like other deer species – both native and introduced – the fallow is today regarded as a crop pest, an unwitting cause of vehicle collisions, and a potential carrier of disease from bovine tuberculosis to foot-and-mouth.

The common pheasant was already successful before its introduction to Britain, having colonised a swathe of Eurasia from the western Caspian region to Japan. As discussed, in Britain its bones first turn up at Roman sites, and historical documents – most of them written after the fact – indicate that pheasants were sometimes eaten as a luxury prior to the Norman invasion. For instance, in 1059, King Harold is said to have offered the bird as a privilege to the canons of Waltham Abbey in Essex, a gift deemed equivalent in value to a brace of partridges or a dozen blackbirds. In 1098, Radulfus, the Prior of Rochester, dispatched to his monks 16 pheasants (along with 1,000 lampreys, 300 hens, 30 geese, 1,000 eggs, 4 salmon and 6 bundles of wheat). A contemporary and perhaps more dependable record – a bursar’s roll at Durham Priory dated to the reign of the Saxon king Edward the Confessor (1042–1066) – includes a purchase of one pheasant and 26 partridge. Pheasants may first have been kept in royal parks and forests, along with fallow deer, and their increasing prominence on banquet menus from the late twelfth century implies that they had by then naturalised. In 1251, Henry III ordered 290 of them for his Christmas feast, and by the late 1400s, pheasants warranted legal protection from the Crown. These early imports were in fact the ‘Old English’, or colchicus, subspecies from the Caucasus and lacked the distinctive white neck ring of the torquatus race, originating in China, which is these days released for shooting.

The pheasant is something of an outlier from this period in retaining a certain aristocratic association. The best explanation is that these poorly camouflaged, clumsy fliers have so far failed to get along in the British countryside, despite repeated reintroduction. Of an estimated 20 million poults (young birds) loosed annually, 90 per cent perish within the year. And not just from the shooting: most evade the guns only to be picked off by foxes or end up as roadkill.

Although pheasants might one day naturalise in Britain, there’s precious little evidence for that so far. The same can’t be said for what is without doubt the most impactful of all medieval introductions.

‘It’s quite a massive hill here, this site,’ I said. ‘And that’s all just made for the rabbits, this big mound?’

‘Well, no. The hill, I think, is natural. It’s just that rectangular mound there that’s made for them,’ responded David patiently.

‘Sorry. I was thinking the whole hill was a warren!’

‘Oh. That would make it the world’s biggest pillow mound, yeah.’

The aroma of wood smoke wafted in the chilly morning air. A distant chainsaw whined. We were standing at the foot of a steep grassy hillock, almost 100 metres high, upon which was broodingly perched a three-storey tower of limestone. Known these days as the Bruton ‘dovecote’ for its later repurposing by pigeon-fanciers, the original function of the pale-yellowish structure, which dates back to the 1500s, is a mystery. One theory has it as the prospect tower for the nearby Bruton Abbey – long since demolished on the orders of Henry VIII during his dissolution of the monasteries – offering the local aristocracy a grandstand view of the abbey’s deer park. But neither doves nor deer, nor indeed the pair of Friesian cows munching contentedly near the base of the tower, had drawn me to South Somerset today.

No, I was interested in rabbits and in particular how and why these shy burrowing mammals from southwest Europe had been introduced to Britain, and then run amok. An important clue was offered by the pillow mound, a characteristic earthwork which to the trained eye shouts ‘rabbit’. Clearly, my eye wasn’t trained because Dr David Gould, a landscape archaeologist from the University of Exeter who had agreed to show me some, needed to point out the example that was right in front of us.

‘You see that ridge coming down the hill?’ he said. ‘That’s one.’

The British population of the European rabbit today numbers in the tens of millions and the species is now regarded as a worldwide menace. Yet the original bunnies were an ineffectual lot, hardly a patch on their vigorous descendants and quite unable to excavate their own burrows. This is where the pillow mounds came in. Created by piling up soil in long, low heaps, and encircled by ditches, possibly to deflect any floodwaters, these artificial structures provided a dry, soft and well-ventilated substrate into which the rabbits could dig. Some even incorporated stone-lined tunnels making life easier still for their feeble tenants. At the same time, pillow mounds concentrated the rabbits in one place for ‘hunting’. If you could call it that. The phrase ‘shooting fish in a barrel’ comes to mind.

The pillow mound was a hallmark of the artificial rabbit warren, or ‘coneygarth’, from the Middle English coning-erth. Coney, coning, conyng, and sundry other derivations thereof, was the original word for the adult animal, the term ‘rabbit’ – from the French rabette – being reserved for juveniles. David had spent three years visiting 650 coneygarths across southwest England, from Cornwall to Wiltshire, racking up more than a thousand pillow mounds along the way. Little wonder he knew one when he saw it.

‘Most are rectangular, like the ones here at Bruton,’ he said. ‘But you get circular ones, oval ones, cruciform ones. Just random, weird little ones.’

I suspected pillow mounds haunted his dreams.

Along with documenting the shapes, David was keen to understand just how conspicuous the pillow mounds were: ‘If you were wealthy, you were expected to have access to these animals. It was kind of like the “in thing”. But I wanted to know whether pillow mounds themselves, as visual components of the landscape, had a symbolic significance in their own right. Was it like parking your expensive car in the front drive to show off?’

In the event, David’s field work revealed no clear pattern: pillow mounds were as likely to be tucked away behind a hill as to be sited ostentatiously on its slopes. It seemed that so long as the lord of the manor could offer distinguished guests fresh rabbit for dinner, whether or not the warren was visible from the manor house was of little concern.

As with other exotic imports, rabbits served multiple functions, offering meat, fur and status. Like pheasants and fallow deer, the association with elites can be traced as far back as the Romans who, elsewhere in their empire, prized rabbit foetuses, known as laurices, as a delicacy and reared the creatures (along with hares) in stone-walled pens called leporaria. The discovery of a fragment of rabbit tibia at Fishbourne, dated to the first century CE, suggests the species was brought to Britain during the Roman occupation, perhaps as a pet. But rabbits don’t seem to have established: there’s no Anglo-Saxon word for them and they don’t get a nod in the Domesday Book. ‘Coney culture’ nevertheless persisted on the continent after the Romans left and, by the Norman period, rabbits had been added to the variety of smaller game that aristocrats would seek permission from the king to hunt under the right of ‘free warren’. (Other free warren species – undoubtedly offering more sport – included fox, hare, wildcat, pheasant and partridge.)

Britain’s current rabbit population dates to the second half of the twelfth century, with animals possibly brought by homeward-bound crusaders. At first, the rabbits were kept on islands off the south coast of England, the benign climate and lack of predators suiting these delicate mammals. Although there’s some dispute about it, the earliest putative record dates to around 1135 when Drake’s Island in Plymouth Sound was said to have been granted to Plympton Priory, cum cuniculus (‘with rabbits’). In 1176, rabbits were being kept on the Scilly Isles, while on Lundy in the Bristol Channel, the tenant was permitted to take 50 a year between 1183 and 1219. One of the earliest allusions to mainland rabbit-keeping dates to 1235 when King Henry II presented ten live coneys as a gift from his park at Guildford.

Soon after the introduction of rabbits to mainland Britain, coneygarth escapees were turning up as pests on nearby arable fields, yet the species remained scarce during the early years. This rarity was reflected in the price, with a single animal costing the same as five chickens. Coneygarths were guarded and poachers subject to the full weight of the law. In England alone, 465 cases of rabbit theft are recorded between 1268 and 1551. Contrary to popular belief, peasants weren’t always – or even mostly – responsible for rabbit-thievery. Break-ins were more often than not the handiwork of fellow landowners in a spirit of aristocratic one-upmanship. Warreners, who were tasked with ensuring the safety of their precious charges, had their work cut out. They constructed lodges and watch-towers to spot poachers, and fitted ingenious vermin traps to divert and capture stoats, weasels and other would-be predators. Trowlesworthy Warren on Dartmoor, which dates back to the seventeenth century, boasted 76 such traps. But not every rabbit predator was quite so unwelcome.

The ferret, a tame version of polecat which originated in North Africa and had been domesticated since the fourth century BCE, appeared in Britain from 1223, soon after the dawn of rabbit-keeping. Warreners co-opted the wiry carnivore to their cause, filing down its teeth and using it to flush bunnies from their burrows. Ferrets also formed an important component of the rabbit-poacher’s toolkit, along with dogs and nets.

Against the odds, the rabbit population started rising, and by the fourteenth century supported a growing export trade in their furs; in 1305, for instance, 200 skins were shipped out of Hull, and by 1398 a certain Collard Chierpetit was granted the right to send 10,000 rabbit pelts to Holland. No fewer than 4,000 rabbits were served at the 1465 investiture of the Archbishop of York and, a century later, the Swiss naturalist Conrad Gesner noted that: ‘There are few countries wherein coneys do not breed, but the most plenty of all is in England.’ It wasn’t until the late 1700s, however, that the wild population properly took off; rabbits had by then evolved into an altogether hardier proposition, able to capitalise on new rotational field systems, which provided a year-round supply of food. The wholesale removal of weasels, pine martens, polecats, stoats, foxes and other predators by gamekeepers tasked with preserving pheasant and partridge, also indirectly benefited the rabbit whose ubiquity helped consign their high-class status to history. Rabbit farming continued in Britain right up to the twentieth century, with numerous large coastal semi-natural warrens in places like Cornwall and South Wales continuing to be protected from poachers, suggesting that the species retained a certain economic value until modern times. Nevertheless, this once-prized commodity fit for a king generally came to be dismissed as a pauper’s ration, and at worst, vermin to be eradicated.

Rabbits have long had religious connotations, most likely anchored in the supposed proclamation of the sixth-century Pope Gregory that rabbits, or more precisely their foetuses, were fit for eating on fast-days. Plucked from the womb’s watery environment, the reasoning went, laurices could be deemed honorary fish, not warm-blooded animals which would have been off limits. But this turns out to be a case of sloppy scholarship: the Pope never made any such decree. Instead, it was his contemporary and namesake, Bishop Gregory of Tours who had pronounced on rabbits, and merely to report on the practice of laurice consumption during Lent. Chinese whispers did the rest.

Writing in the 1990s, the archaeologists David and Margarita Stocker nevertheless detected an allegorical significance in ‘defenceless’ communities of rabbits being ‘herded and managed like sheep’ by a Christ-like warrener, before emerging ‘from the ground to fulfil themselves’. Warming to their theme, the Stockers evidenced the deliberate, prominent and ‘symbolically meaningful’ placement of pillow mounds within monastic precincts at Sawtry Abbey in Cambridgeshire, Nun Coton Priory in Lincolnshire and Croxton Abbey in Leicestershire. In his own documentary research on rabbits, however, David Gould has found little to bolster, or at least privilege, the sacred connection. ‘In the medieval period it’s basically the elites who first owned rabbits,’ he said, ‘and that meant both lay and clerical elites. In fact, when you look back through the records, warrens are more often linked to secular aristocracy.’

As it happened, Bruton had something to say on fish too (another reason David had suggested we meet here). We trudged to the crest of the dovecote-dominated knoll which gloried in the name of ‘Lusty Hill’. Was this a reference to the renowned reproductive capacity of its former livestock? That was a question for another day. Passing two smaller pillow mounds on the summit, we descended the far side to a series of boggy depressions, the remains of ancient and overgrown ponds. ‘I’m not an expert, but I think they’re medieval and older than the pillow mounds,’ said David. These artificial pools – fed by a stream which flows on to the River Brue – once supplied fresh fish to Bruton Abbey.

Whether or not rabbits were regarded as fish and kept and eaten for their ecclesiastical significance is unclear, but actual fish certainly were favoured by religious orders across continental Europe and, between the ninth and eleventh centuries, appeared ever more prominently on the table at Benedictine monasteries. The stricter regimes at Cistercian and Carthusian communities resisted even fish but later allowed the consumption of small quantities, or ‘pittances’. The medieval period coincided with a massive expansion of marine fishing which targeted herring, cod and hake. While coastal communities enjoyed fresh catch, those living far inland had to make do with salted or dried fish. The elites, though, abhorred preserved fish and instead focused on locally caught freshwater species, like eels, which were trapped as they migrated up or downstream. The younger specimens were grown in stock ponds, either purpose-built or adapted from existing millponds, moats and former river channels.

Meanwhile in Britain, the eating of fish also grew in popularity in the centuries following the Norman Conquest. The people of this island nation had always enjoyed access to seafish, but the continental pond culture centring on freshwater varieties was nevertheless imported, as much for its prestige as for its nutritional benefits. Like deer parks and coneygarths, Britain’s fishponds were first associated with the wealthy, and by 1300 could be found on the estates of clergy, aristocratic landowners and the Crown from Wiltshire to Yorkshire – the ones at Bruton being surviving examples. In time, husbandry techniques advanced enough to provide a steady food source and aquaculture became a widespread commercial enterprise, although freshwater fish retained its cachet. The sorts of fish best able to endure the warm, slow-moving, turbid and oxygen-poor water of medieval ponds were favoured. That meant roach, tench, chub, dace, perch, and especially pike and bream. To this roll-call of hardy natives would later be added a foreign fish whose origins are as murky as the waters it frequents.

The common carp is today among the world’s most important food fishes. Three million metric tonnes are grown annually across 100 countries, equivalent to a tenth of all freshwater aquaculture production. It’s easy to see why: the fish breeds and grows fast, tolerates a wide variety of environmental conditions and eats pretty much anything that can be sucked up by its telescopic mouthparts. The koi carp, a colourful variant developed in a mountainous region of Japan, is perhaps the world’s most popular outdoor ornamental fish and almost as well travelled as its edible cousin. Meanwhile, the species supports an angling market which in Britain alone is worth close to a quarter of a billion pounds each year.

The ancestral common carp evolved close to the Caspian Sea around 2.5 million years ago and, taking advantage of the proliferation of waterways during warmer interglacial periods, expanded its range east into mainland Asia and west to the basins of the Black and Aral Seas. The European version of the common carp appeared in the Danube river some 10,000 years ago. And there the fish might have stayed were it not for its discovery by the Romans – keen aquarists – sometime in the first or second century CE. (Carp bones dated to that period have been identified at the site of a former Roman frontier fort near Iža in Slovakia.) Able to survive out of water and without food for prolonged periods, the carp were transported, possibly wrapped in wet moss or sacking, to the piscinae (reservoirs) of Italy as gourmet items and pets.

Carp however, live specimens at least, weren’t present in Roman Britain, and don’t feature in European pond culture until around the twelfth century. The first written reference on this side of the Channel comes from the kitchen accounts of King Edward III at Canterbury, dated to 1346, which show a carp and eight pike costing 22 shillings. The carp in this case was probably an imported specimen, because the fish doesn’t seem to have been stocked in this country for another century. In 1496, The Boke of St Albans – attributed to Dame Juliana Berners, prioress of Sopwell nunnery – describes the carp as a ‘deyntous [delicious] fisshe’, and then in 1532 ‘Carpes to the King’ appears in Henry VIII’s Privy Purse expenses for that year.

Despite this, carp was historically less important in Britain than elsewhere, perhaps because by the sixteenth century improvements in navigation and ship technology were, for the first time, allowing exploitation of vast new shoals of marine fish from offshore Atlantic waters. The common carp nevertheless qualifies as among the first non-native fish to have naturalised in Britain and remains abundant in still and slow-flowing waters across England, with scattered populations in Wales and Scotland. The species is often accused of muddying the water as it ploughs river and lakebeds for invertebrates, fish eggs and other buried morsels. The resulting high water-turbidity stops light penetrating and interferes with photosynthesis, messing up food webs. But carp enthusiasts, of which there is a growing army in Britain, argue that recreational boating and other human activities are as much to blame.

A fascination for all things botanical, both native and exotic, also germinated within the monasteries and aristocratic households of Britain during medieval times; commercial horticulture can be traced to the thirteenth century, with enterprises in London and Oxford selling seeds in large numbers. Husbandry, a set of rules for estate management by Sir Walter of Henley published in 1280, states that imported corn-seed often outperforms home-grown counterparts, and this influential work may have encouraged the acquisition of foreign plants. By the late 1300s the Dominican friar and herbalist Henry Daniel was nurturing 252 sorts of herb in his garden in Stepney, London, of which 100 were non-native.

Plants were cultivated primarily for function not aesthetics, although the beauty of snapdragons, snowdrops and snake’s head fritillaries – all of them apparently introduced during this period – is undeniable. Dill, coriander, summer savory, black mustard, fennel, caraway and parsley were all condiments whose use had declined after the Romans left but which made a big comeback during medieval times. Hitherto unknown species also arrived including saffron, a luxurious yellow spice made from the dried stigmas of a crocus flower. The plant originated in western Asia and is first recorded in England in the fourteenth century. Used as culinary ingredient, dye, perfume and aphrodisiac, saffron was famously grown in East Anglia, its economic significance such that a major centre of production, the Essex town of Walden, adopted it as a prefix in the sixteenth century.

Horticultural introductions served other purposes. As its name suggests, the leaves and roots of soapwort, a member of the pink family native to the Middle East, contain natural detergents. Appearing in Britain from medieval times, soapwort found use in the wool trade, washing not just woollen products but the sheep from which they were derived; as recently as the 1970s, extracts were employed to clean fragile tapestries. Chasteberry, a type of vervain with purple flower cones which originates in the eastern Mediterranean, was used in monasteries to suppress libido among the acolytes, and nuns stuffed their bedding with the aromatic leaves to quash wicked urges. (The ancient Greeks prized the plant for the reverse effect: women slept on it to enhance their fertility.) The Aegean wallflower, meanwhile, was esteemed for the fragrance of its vivid golden blooms, reminiscent of violets. In its home range, the plant spreads over cliffs, and may have first reached Britain stuck to building stone imported by the Normans. It’s still found clinging to ancient edifices from Bury St Edmunds Abbey in Suffolk to Northumberland’s Lindisfarne Priory.

Almost every introduced plant offered some or other kind of therapeutic function. Gout was treated with wall germander, a variety of mint; feverfew, in the daisy family, was a traditional painkiller; hollyhock, a laxative. Many plants were considered panaceas. Sweet cicely, a celery relative whose strong scent called to mind myrrh, was one of countless such ‘cure-alls’ and was used to remedy rheumatism, cleanse cuts and salve sore throats. It could relieve asthma, cure snakebite and promote sleep. Sweet cicely even stopped you farting. From time to time, serious mistakes could be made: to medieval midwives, the pretty yellow flowers of birthwort, a variety of clematis, resembled wombs – one shudders to imagine how they would know that – and they would administer its sap during labour to expel the placenta. It turns out that birthwort extracts are carcinogenic and may have killed thousands of women over centuries of misuse.

Such cases were rare however, and did little to disillusion medieval herbalists. Yet, in the fourteenth century there arrived in Britain a disease – caused by one non-native and apparently carried by others – which even sweet cicely would be powerless to prevent (although people gave it a go). It would help change the course of human history, disrupting existing power structures and kick-starting an era of empire building and world exploration to dwarf anything achieved by the Romans and Normans. And the unprecedented globalised trade and migration that resulted would turn a trickle of non-native species into a deluge.

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