Invasive Aliens. Dan Eatherley

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.

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       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