Flies thrive in the warm, humid weather caused by global warming

Scientists at the University of Southampton are predicting the fly population is to soar by 97%, posing a widespread risk to human health.

Dr Dave Goulson led the four-year study at a dozen landfill sites, which were plagued by flies every summer.

He told BBC News Online: "A small increase in temperature gives whopping great increases in fly numbers."

Dr Goulson, a biological scientist, warns that a bigger fly population may lead to spiralling cases of food poisoning in humans.

Some types of food poisoning, normally not seen in winter, could happen all year round Dr Dave Goulson Southampton University

He says warmer weather will also lead to large rises in other insect pests, including some never before seen in the UK.

The findings - based on research at landfill sites in Hampshire and the Midlands - come after UK wasp numbers rose to a 20-year high this summer.

Dr Goulson told BBC News Online: "Some of the main food poisoning bugs are thought to be carried by flies, so more flies mean small epidemics could become much bigger.

"Traditionally, the cold British winter killed off most insects and it took them until well into the spring to recover their numbers, but milder weather has seriously affected this cycle.

"This means outbreaks of some types of food poisoning, normally not seen in winter, could happen all year round.

Continental invasion

"We have already seen continental insects invading Britain, such as termites and a new species of wasp.

"If temperatures continue to rise, it is very likely that we will start to see insects like the Colorado potato beetle, which wipe out potato and bean crops on mainland Europe."

Dr Goulson says fly numbers could be cut by composting waste like kitchen scraps and garden clippings, instead of sending it to landfill, where it provides rich food for flies.

He added: "Unfortunately flies have become resistant to most insecticides, but simple old fashioned things like fly paper and keeping food covered still do the job."

Some scientists predict at least a three-degree rise in average world temperatures in the coming decades, even if emissions of greenhouse gases were halted immediately.