Sir David Attenborough urged people to take part in a nationwide count of butterflies to help find out if the hot, dry spring has hit the "bewitching" insects.

The naturalist, who is president of wildlife charity Butterfly Conservation, said butterflies were one of the "stars of the British countryside", but warned they were in long-term decline.

And in the wake of one of the hottest and driest springs on record, with some areas of the country hit by drought, the nationwide survey is important to find out how butterflies are faring, Butterfly Conservation said.

The wildlife charity wants to see whether butterflies, many of which emerged much earlier than usual as a result of the hot, dry conditions, have managed to turn round declining fortunes or have starved as the plants they feed on wilt in the drought.

Butterfly Conservation is running the annual Big Butterfly Count until July 31, and is urging the public to take 15 minutes in a sunny place to count all the butterflies they can see, and then submit their sightings online. The results will help conservationists see the impact of the unusual spring weather, as well as track the progress of garden favourites such as the small tortoiseshell and the peacock butterfly, which have seen populations plummet.

Sir David said: "Summer just wouldn't be summer without butterflies. But they continue to be in long-term decline.

"It's more vital than ever to know where they can be found and in what numbers.

Last year's count, in which 10,000 people recorded 189,000 butterflies, revealed that the most common butterfly in Britain, the meadow brown, had its worst year on record but the common blue had a very good summer.

This year, the count is focusing on 19 species including a couple of day-flying moths, and a downloadable chart is available to help people identify them.

n Go to www.bigbutterflycount.org