Bloodsucking fly moves into towns as Britain warms up

A blood-sucking female horsefly, five times larger than normal, has been sighted in urban Britain for the first time. The one-inch-long Tabanus bovinus can eat through cow hide and regularly causes cattle to stampede. Its bite can leave a swelling the size of a tennis ball on a human arm.

A blood-sucking female horsefly, five times larger than normal, has been sighted in urban Britain for the first time. The one-inch-long Tabanus bovinus can eat through cow hide and regularly causes cattle to stampede. Its bite can leave a swelling the size of a tennis ball on a human arm.

The horsefly, although rare, has been found in rural areas of the UK but never before in centres of population. Experts suspect that climate change is responsible for alterations in its behaviour and that of many other insects.

A wet summer, as this summer has been, is not necessarily a cold one. Last year, for example, was Britain's hottest since records began in 1659, even though there were no heatwaves and no single month broke a record for temperatures. Now, the combination of warm and rainy weather appears to have created perfect conditions for Tabanus bovinus. The species has been spotted in urban areas of Devon. It traditionally favours peat bogs, and colonies are found in the New Forest where the females feast on the pony population.

Brian Eversham, conservation director with the Wildlife Trusts, said: "I'd be surprised if this horsefly could live and spread in towns - it's more likely they have been blown or flown there - but many movements are prompted by peculiar weather conditions.

"The question is whether this is all down to a spell of odd weather or if it's long-term climate change. My money is on it being part of a longer-term trend. So many organisms are responding to it. Insects grow faster in hot weather, and fly farther. They also breed in greater numbers resulting in overcrowding and that is another incentive to move on."

Climate change is also being cited as the reason for the migration of less harmful species of the fly family. The British Dragonfly Society has found that many dragonflies are moving north as the climate of northern England warms up. Southern England is the traditional northern limit for dragonflies in Britain but the migrant hawker has been found in Teesside while the ruddy darter has become established in the North and is now colonising the Borders.

"Global warming is the most obvious answer," said Bill Wain, secretary of the society. "Dragonflies are a tropical species and a migrant species, but if it were too cold for them they wouldn't move there."

The news is an additional concern over dragonflies. Last week, entomologists at the University Museum in Oxford found that many species, along with beetles, butterflies and bees, have not been seen for years. The disappearance of these and other insects is a worry because they form some of the basic links at the bottom of the food chain.

Mr Eversham is sceptical that climate change may be directly affecting these dragonflies, but believes other insects may be faced with problems. "These particular dragonflies have a southern limit of North Africa, so it's unlikely they are finding southern England too hot," he said.

"But species that live in the North already may have difficulties. If you live on top of a mountain in Scotland or Wales and it gets too hot, then there's nowhere else to go."