Kitabı oku: «Invasive Aliens», sayfa 4
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.
