Butterflies are “failing to cope” with climate change and the pollution of the British countryside, experts have warned after a disastrous year saw population declines in 40 out of 57 species.
The UK Butterfly Monitoring Survey found it had been the fourth-worst year overall with six species – the heath fritillary, grizzled skipper, wall, grayling, white-letter hairstreak and white admiral – all suffering their most dramatic declines in the 41 years since records began.
Sixteen species saw increases with one remaining about the same, the annual survey found.
But Professor Tom Brereton, head of monitoring at Butterfly Conservation, said the results showed that the insects were in trouble.
“Worryingly, not even the pleasant summer weather of 2016 was enough to help butterflies bounce back from a run of poor years,” he said.
“The results show that butterflies are failing to cope with our changing climate and how we manage the environment.
“As butterflies are regarded as good indicators of environmental health this is hugely concerning for both wildlife and people.”
A mild winter is thought to have been the beginning of their troubles.
Research has suggested this leads to an increase in diseases and predation and a disruption of their over-wintering behaviour.
This was followed by a cold spring, which caused further problems as it can delay their emergence into the winged stage of their life, leading to shorter lifespans.
Some of the declines in population numbers found by the survey before were jaw-dropping.
The gatekeeper was down 48 per cent on the year before, while other similarly widespread species like the meadow brown and wall butterfly (both down 31 per cent) also struggled.
The white admiral, white-letter hairstreak and grayling numbers also fell by 59 per cent, 42 per cent and 27 per cent respectively.
The heath fritillary, now found in just a few sites in southern England, fell by 27 per cent between 2015 and 2016, raising fears for its long-term future in the UK. Its numbers have fallen by 82 per cent in the last 10 years.
Dr Marc Botham, butterfly ecologist at the Centre for Ecology & Hydrology, which was also involved in the survey, said: “The weather at critical times of species development can cause dramatic changes in population numbers in the short term.
“What is of greatest concern is the regularity with which these short-term changes in recent years are negative, resulting in significant long-term declines for many species.
“Furthermore, this is becoming more and more commonplace for many of our most widespread and abundant species equating to large reductions in overall butterfly numbers with knock-on effects to their ecosystems.”
On the positive side, the large blue, which was reintroduced after extinction in the UK, recorded its second best year on record with numbers up by 38 per cent on 2015 after conservation work to improve the type of grassland habitat the still-rare insect needs.
The widespread red admiral recorded a rise of 86 per cent compared to 2015 and the clouded yellow, another mainly migrant species, saw its numbers rise by 35 per cent.
Anna Robinson, monitoring ecologist at the Joint Nature Conservation Committee, thanked people for helping carry out the survey.
“We are really grateful to the thousands of volunteers who get involved in monitoring the UK’s butterflies,” she said.
“The evidence provided by the [survey] is of great importance in showing the need for conservation action to improve the situation.”
The survey has run since 1976 and involves thousands of volunteers collecting data through the summer. Last year a record 2,507 sites were monitored across the UK.
The scheme is organised and funded by Butterfly Conservation, the Centre for Ecology & Hydrology, the British Trust for Ornithology and the Joint Nature Conservation Committee.