Common blue butterflies were the biggest losers from the coldest summer for almost two decades, with numbers tumbling by almost two-thirds, experts have said.
The results of the Big Butterfly Count 2011 revealed that the number of individual butterflies seen by each person counting the insects was down 11 per cent on last year.
The common blue saw numbers tumble by 61 per cent in the count, which involved more than 34,000 people across the country recording sightings of 322,000 butterflies.
Experts at wildlife charity Butterfly Conservation say they had expected a bumper summer for butterflies after a record-breaking hot, dry spring, but the cold summer with prolonged spells of rain hit the insects.
In cold, rainy weather they are unable to fly, feed, find mates or lay eggs.
It was not all bad news for butterflies though, with perennial garden favourite the Red Admiral numbers almost doubling (up 98 per cent), while small tortoiseshells saw their numbers stabilise after recent severe declines.
The small tortoiseshells also experienced something of a north/south divide with three times as many of the butterflies recorded per count in Scotland than in England.
The gatekeeper butterfly rose three places in the top 10 most commonly seen butterflies to top the poll with more than 52,000 spotted, but numbers of the butterfly were down 12 per cent on last year.
Other commonly recorded species included the small white, the large white, the meadow brown, the red admiral and the peacock.
Richard Fox, Butterfly Conservation surveys manager, said: ”The fantastic response of the UK public to Big Butterfly Count 2011 has given us a detailed snapshot of how butterflies fared this summer. Twice as many counts were carried out this year as in 2010.
”Unfortunately, the results show that it was a poor summer for butterflies with many species showing declines compared to last year.
”The dismal summer weather, the coldest for 18 years, is undoubtedly to blame, although many butterflies have suffered long-term declines as a result of destruction of their habitats by human activities.”
He added: ”In bad summers, butterflies need all the help they can get from people to maintain their breeding areas.”
Butterfly Conservation warns that the last four years have seen butterfly numbers plummet to an all-time low, and that almost half of the 59 British species are now under threat.
Butterflies are also an indicator of the health of the wider countryside because they are sensitive to environmental change.