Nearly 40,000 conservation-minded drivers counted the bugs splattered on their vehicle number plates this summer, the Royal Society for the Protection of Birds (RSPB) announced yesterday.

Nearly 40,000 conservation-minded drivers counted the bugs splattered on their vehicle number plates this summer, the Royal Society for the Protection of Birds (RSPB) announced yesterday.

The motorists were helping the world's first mass survey into possible insect decline, a UK-wide Big Bug Count held throughout June, and the initial results appear to confirm suspicions that insect numbers have fallen, the RSPB said.

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Using a cardboard counting-grid dubbed the "splatometer", they recorded 324,814 "splats", an average of only one squashed insect every five miles. In the summers of 30-odd years ago, car bonnets and windscreens would quickly become encrusted with tiny bodies.

"Many people were astonished by how few insects they splatted," the survey's co-ordinator Richard Bashford, said.

People were asked to wash their number plates, drive for between 20 and 80 miles, and count the insects on the plate, using the grid to make counting easier. The study was prompted by fears that a decrease in insect populations could cause problems for birds which rely on them for food.

Swallows and house martins are specialist insect feeders, and seed-eating birds, such as skylarks and house sparrows, both in decline, need insects to feed to their young. Numbers of many bird species have been dropping alarmingly, and the house sparrow population has crashed by 65 per cent in the past 31 years. Theories abound about why insect populations seem to be declining, and include habitat loss and pesticides.

Mr Bashford said. "variation in insect numbers across the UK was small, but there appears to be a gradual increase in numbers from the South-east of England to Scotland. The reasons for this, and the potential consequences for birds, will be the focus of future research."

The RSPB plans more "splatometer" tests to gather more data.