Numbers of the delicate wood white were down by 66 percent last year on dismal 2007; its population has slumped by 90 percent over the long-term recording period. The duke of burgundy and the high brown fritillary are most at risk of extinction. The high brown survives in just 50 small sites: at one spot in Dartmoor, southwest England, there were 7,200 in 1995; last year, there were just 87. Nationwide, numbers have fallen by 85 percent over 10 years.
?his run of bad weather has really pushed those species to the brink in many areas,?says Martin Warren, the chief executive of Butterfly Conservation.
Butterflies find it difficult to fly, feed and mate in bad weather, but these figures are not just a seasonal blip caused by freakishly soggy summers. The 苞ollecting of British butterflies has ceased to be acceptable and yet butterfly populations have still plummeted. Far more devastating than unscrupulous collectors of old has been industrial agriculture and the loss of 97 percent of England's natural grassland and wildflower meadows; planting conifers or letting our broadleaved woodlands become too overgrown for woodland flowers; and the sprawl of motorways and urban development.
To this deadly cocktail has been added a new poison: climate change. In theory, a gentle global warming should benefit almost all of Britain's butterflies. Creatures of sunshine, most of our butterflies are found in southern England, where many are at the limit of their natural range; as our summers become hotter, these butterflies should thrive and spread further north. There are a few winners already: the beautiful comma is moving north and the rare silver-spotted skipper has done well thanks to hotter summers. Britain may also be visited more regularly by exotic species that were once rare migrants.
The fate of one much-loved native shows that this happy outcome, however, will not come to pass for most species. The small tortoiseshell is the labrador of the butterfly world: cheerful and content to live close to humans. Its caterpillars devour ubiquitous nettles. As an adult butterfly, it feasts on suburban flowers and hibernates in garden sheds, pitter-pattering against our windows when spring comes round again. Thanks to climate change, it is spreading north and is now seen for the first time in remote parts of Scotland. Unfortunately, so too is Sturmia bella (how the person who named this ugly brute could call it beautiful is beyond me), a species of parasitic fly.
This nasty fly was recorded for the first time in Britain in Hampshire, southern England, 11 years ago. By last summer, it had reached Merseyside, northwest England, thanks to a modus operandi every bit as gory as the Alien films. It lays its microscopic eggs on patches of nettles where small tortoiseshell caterpillars feed. These unwittingly eat the fly? eggs which become tiny worms inside the caterpillar, bursting out of their bodies just when the small tortoiseshell is beginning its miraculous transformation into a butterfly inside its chrysalis.
Last year was the worst ever year for small tortoiseshells, its population slumping by 45 percent compared with 2007, despite thousands of migrant small tortoiseshells arriving from Europe in September. In southern and central England, it appears to have been virtually wiped out: during my afternoon roaming the Chilterns last week, I saw 10 peacocks and 12 yellow brimstones and the odd rather more elusive species, such as the grizzled skipper, but not a single small tortoiseshell.