There's only one possible reaction when you first see it. What the hell is that? It looks like a bee but it's bigger than any bee you've seen before, and it doesn't have bee-type yellow and orange stripes - it appears to be deep blue, all over, as it lumbers through the air.
It's about three times the size of the biggest bumblebee. It may have astonished you on a holiday in the Med or other warm climes but otherwise you're unlikely to have encountered anything like it. But now you can see it in Britain - for the violet carpenter bee, the biggest and most remarkable-looking bee in Europe, has crossed the Channel and has begun breeding in this country.
Take heart. Even though it is one of the scariest-looking insects you're ever likely to catch sight of (typically measuring at least 25mm in length but appearing considerably larger in flight), it is the violet, not the violent carpenter bee. A killer bee it is not; it is not aggressive and is unlikely to sting you. The name comes from the violet wings, which appear to give a blue sheen to its black body when in flight.
In the past century, it has occasionally strayed to Britain, and has made one or two unsuccessful breeding attempts but now, to the intense excitement of Britain's entomological community, it has become established. A colony has been set up and is thriving in a dead Bramley apple tree, in the garden of retired company director Derick Walton and his wife Janet, in Shepshed, near Leicester. The bees first appeared last summer. Remarkably, they have survived the winter and appear to be flourishing.
The reason, almost certainly, is climate change. The appearance here of Xylocopa violacea is simply the most vivid example yet of the phenomenon of insects from continental Europe moving north into Britain as the climate warms.
In the past decade, a whole series of continental bees, wasps, moths, dragonflies and grasshoppers has appeared here, and their arrival has been closely monitored by the well-known naturalist Peter Marren. "It's an increasingly-obvious phenomenon," he said. "New insects from continental Europe are appearing here more and more, and it's virtually certain that climate change is responsible. Each insect has its own story, of course, but the thing that's propelling the entire phenomenon is the warming climate, without a doubt."
Of the violet carpenter bee, Mr Marren said: "It's going to come as a bit of a shock to people in Britain, as it's so much bigger than any of our native bees, and we've got some really big bumblebees - but they're nothing compared to the violet carpenter bee. It's an incredible size - a colossal great thing."
Several continental bees and wasps have set up home in the UK in recent years, some so unfamiliar that they do not yet even have English common names, such as the large social wasp Dolichovespula media, which created widespread concern among gardeners when it first arrived in the UK in about 2000 because of its size. It is bigger than any British wasp, and will sting if disturbed.
Other wasps that have recently come into Britain include the bee-wolf Philanthus triangulum, which hunts bees for food, and the French spider-eating wasp Episyron gallicum, newly discovered breeding in Bedfordshire, which catches spiders, paralyses them with a sting, and lays its eggs on top of them - so the wasp larvae feed on living spider.
A rather less scary arrival is the brown-banded carder bee, Bombus humilis - a continental species that has now begun breeding on brownfield sites in the Thames estuary.
The situation is similar with lepidoptera (moths and butterflies). The charity Butterfly Conservation has been tracking the new moths arriving in Britain; it reckons we have been getting about one new species a year from the Continent for the past decade. Most are perfectly benign (with their curious names, such as Clancy's rustic or Langmaid's yellow underwing) but one species in particular, the horse chestnut leaf-miner moth Cameraria ohridella, first recorded in Wimbledon in 2002, has now attacked conker trees all across southern England, making their leaves appear brown and wilted in summer.
A much more attractive moth occurrence has been the increase in numbers of the charming hummingbird hawk-moth Macroglossum stellatarum, which does indeed move in and out of flowers, seeking nectar, just like a hummingbird. These moths have always visited Britain but now they are overwintering as adults and successfully breeding here. Last year, thousands were visible right across the country, as far north as Scotland. "You couldn't miss the hummingbird hawk moths last summer," Peter Marren remarks.
Two butterfly species, once annual migrants from Europe, have also started overwintering in Britain and can thus now be considered resident species - the red admiral Vanessa atalanta and the clouded yellow Colias croceus. The fact that red admirals are now surviving the winter (as adults) is the reason so many of them are being seen in early spring. Clouded yellows are now surviving the cold months as caterpillars and the larvae have been found on the undercliffs at Bournemouth - one of the country's warmest spots.
The list goes on and on. Several new dragonfly and damselfly species have been found breeding in Britain in the past 10 years, ranging from the small red-eyed damselfly Erythromma viridulum first recorded in the UK in Essex in 1999, and now breeding as far north as the Midlands, to the lesser emperor dragonfly Anax parthenope , usually thought of as a Mediterranean species, first recorded in the Forest of Dean, Gloucestershire, in 1996.
Until last year, perhaps the most spectacular insect new arrival was the sickle-bearing bush cricket, Phaneroptera falcata, a large green grasshopper-relative which turned up last summer in Hastings Country Park, breeding on rosebay willowherb.
But now we have the violet carpenter bee to top the lot. To their astonishment, Mr and Mrs Walton first noticed several of the bees buzzing around the dahlias in their large wildlife-friendly garden (hedgehogs, rabbits, foxes) last July; later they realised the bees had made a nest in the dead apple tree. Eventually, their daughter Julie identified the beast from an insect field guide, and their son Robert managed to get pictures of the big bee.
After they realised the bees had survived the winter, they posted a notice on a wildlife website, which created great excitement, not least in BWARS - the Bees, Wasps and Ants Recording Society. Lizzie Peat, an entomologist for Leicestershire County Council and a BWARS member, visited the garden and made a positive identification, which other BWARS members have confirmed. "It's very exciting," said Ms Peat.
When The Independent visited the garden this week we got several glimpses of Xylocopa violacea - and we can say without fear of contradiction that, besides symbolising a whole new era in British wildlife, it is quite some bee.
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