Last summer’s drought may have reduced butterfly populations this year because grasses and flowers that would usually feed caterpillars withered and died in the heatwave, scientists say.
People are being urged to help researchers understand the impact of extreme weather on British butterflies by counting the number and species they see this summer as part of the world’s largest insect survey.
The Big Butterfly Count runs for three weeks from Friday. Members of the public are asked to spend 15 minutes in a local park, garden or green space recording the butterflies they see.
So far this year, numbers of common butterflies including small tortoiseshells and peacocks whose caterpillars were feeding on nettles late last summer are significantly lower than normal.
Dr Zoë Randle, a senior surveys officer at Butterfly Conservation, said: “What we’re really concerned about is the survival rates of caterpillars from last summer. Small tortoiseshells have had a dreadful year so far, as have peacock butterflies, and the whites are doing quite poorly as well.
“We want people to take part in the count to generate really important data so we can get a handle on how last summer’s drought affected butterfly species.”
There are fears that grass-feeding species have been struck particularly severely by last summer’s heatwave, which turned the grass brown in meadows, fields and parks. Many experts are reporting lower numbers of ringlets than usual, but apparently good numbers of meadow browns and marbled whites have emerged earlier than normal. The Big Butterfly Count will help establish whether or not these species are bouncing back.
Randle said that after the 1976 drought it took many of these widespread butterfly species a decade to recover their numbers.
With many butterfly species in Britain at the northern edge of their European range, a warming climate should boost their numbers, but data shows that 80% of Britain’s 59 species are declining in either abundance or distribution, with butterflies vanishing from half the places where they once flew since 1976.
Last year’s Big Butterfly Count produced the lowest abundance of butterflies in the 13 years of the popular survey. Conservationists attribute these declines to a combination of habitat loss, industrial farming and climatic changes. As temperatures rise, many butterflies cannot move north across inhospitable farmland to find suitable new sites, although a few more mobile species such as the purple emperor and the comma are managing to do this.
The impact of last year’s record-breaking temperatures and drought may not be the same everywhere, with a north-south divide emerging in the Big Butterfly Count in recent decades. Once ubiquitous garden species such as the small tortoiseshell – whose caterpillars feed on nettles – have become relatively scarce in southern Britain but the butterfly has been much more widely recorded in Scotland and Northern Ireland.
Last year there were almost 100,000 15-minute counts, with participants spending a combined total of 2.5 years looking for butterflies. The count, which is run by Butterfly Conservation, is supported by Sir David Attenborough, King Charles and Chris Packham, who launches it this year, and the information gathered helps inform conservation projects as well as the government’s conservation priorities.
