By Richard Black
Environment Correspondent, BBC News website
Fly populations in Britain could soar this century because of climate change, according to a new study.
Houseflies and bluebottles reproduce more quickly in warmer temperatures.
Using computer models, researchers at Southampton University calculated that fly and bluebottle populations could rise by nearly 250% by the year 2080.
Writing in the Journal of Applied Ecology, they warn this might lead to a rise in infections transmitted by insects, including diarrhoeal disease.
"The rate at which they reproduce is closely linked to temperature," said Southampton's Dave Goulson, "particularly the time interval between an egg being laid and that egg turning into a fly.
"At the optimum temperature of around 32C, it's about 12 days; but in cooler temperatures it can take a month," he told the BBC News website.
"Our modelling shows that a small rise in average temperatures of 2-3C would lead to a big increase in the fly population, which is quite alarming."
The period during which flies are around would also lengthen.
A rise in the fly population could lead to a greater incidence of fly-borne disease, such as stomach upset and diarrhoea.
The most common cause of diarrhoea in Britain is Campylobacter, a family of bacteria.
According to figures from the Health Protection Agency, the number of cases has risen significantly in recent years, from 28,761 in 1988 to 46,178 in 2003.
The rate at which flies reproduce should speed up, according the modelling
Flies are thought to transmit the bacteria, either by carrying small quantities of contaminated material on their bodies or by regurgitating or defecating on to food.
Research published earlier this year showed a strong correlation between the reproductive rate of flies and the incidence of Campylobacter infection.
Nature does provide controls on flies and bluebottles, such as spiders and swallows; but Dave Goulson does not believe their populations would be able to increase enough to keep the flies down.
"There are things that we can do though," he said, "such as covering food in the summer, and taking more care with barbecues and so on.
"The other thing is that a lot of flies breed in organic waste which people throw away into their dustbins. If more people composted, the amount of that waste would be reduced."
Two years ago a World Health Organization study concluded that, globally, climate change has the potential to affect the health of millions; for example, through the spread of disease-carrying insects.