Invasive Aliens

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.