Dan Eatherley - Invasive Aliens: The Plants and Animals From Over There That Are Over Here

Dan Eatherley is a British naturalist, writer and environmental consultant. Since 1995 he has made wildlife documentaries for the BBC with Sir David Attenborough; written on natural history and science for outlets such as Scientific American, New Scientist, BBC Wildlife, the Guardian and the New York Post; and conducted many technical and market research projects on environmental sustainability issues for the UK government, the European Commission and the UN Environment Programme.

Todays countryside is filled with squirrels and sycamores, ladybirds and pheasants, even Canada and Egyptian geese arent out of place. The British Isles have been colonised by a succession of animals, plants, fungi and other organisms that apparently belong elsewhere. Indeed, its often hard to sort out the native from foreign. Some species, like the Asian hornet, cause problems; others, like snowdrops and daffodils, are cherished.

Non-native organisms, invasive or otherwise, from rabbits to rhododendrons, mink to muntjac, hold up a mirror to our own species. The pace of invasion is now higher than ever, but non-natives, problematic or peaceful, arent a modern phenomenon. From the earliest settlement of our islands and first experiments with farming, through the Roman and medieval times, to the age of exploration by Europeans and the current period of globalised free-for-all, the story of invasive species is the story of our own past, present and future.

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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 gardens 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 weve 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 governments 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. Its 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 hornets 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 arent detected and destroyed fast enough.

And thats 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 isnt 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.