Lack of insects devastates bat population in London

The bat population in London has plummeted by 38 per cent since the 1980s, researchers have discovered.

A new report, using research from the Bat Conservation Trust and London Bat Group, has found that the species has been declining in parallel with the house sparrow, perhaps for the same reason: a diminishing supply of insect food.

Bats were once common in well-populated areas. In the 1930s, scores of them could regularly be seen swirling round St Paul's Cathedral. It is not known how numerous they were, but numbers were probably much lower by the time the Greater London Council funded a 1980s study after they became protected under the Wildlife and Countryside Act.

Since then, their numbers have slumped again. The new report, published in the British Wildlife journal, links the decline to a fall in the number of insects in the last 50 years. It quotes Richard Fitter, the distinguished London naturalist and author who in 1945 wrote of "flies that flourish on refuse, horse droppings and various unsavoury paraphenomena of town life".

But bats have faced other problems, notably London being bathed with light at night, said Pete Guest, one of the report's authors. "Bats no longer fly around St Paul's – which is floodlit at night – or the streets. Some species, such as the pipistrelle, won't emerge until it is sufficiently dark, so a lot of lighting is going to shorten their feeding time.

"There are places where it seems like daylight all night and this feeding habitat reduction explains why bat swarms cannot be seen in London these days – not even along the Thames, where they used to gather in great clouds." However, smaller bat assemblies still occur on Hampstead Heath and Wimbledon Common, and conservationists hope they can provide the basis of a comeback.

Mr Guest, a London Wildlife Trust Conservation Officer, said: "We can't return to times when lots of horse manure lay in the streets, attracting flies, but we can boost the insect supply in open places through habitat improvement."