Farmland butterflies bounce back

Small tortoiseshell on barley

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Farmland butterflies have flourished thanks to last year's hot summer, the charity Butterfly Conservation says.

The annual Wider Countryside Butterfly Survey (WCBS) recorded almost double the number of insects compared with the previous year.

Long, sunny periods provided perfect breeding conditions for some of the UK's brightest species, it suggested.

But experts warned the mild winter could reverse the insects' fortunes if they emerged too early for spring.

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The survey has been run by Butterfly Conservation, the British Trust for Ornithology and The Centre for Ecology and Hydrology since 2009.

Last year, volunteers monitored 850 randomly selected 1km squares across UK farmland.

With more than 70% of the UK's land area devoted to agriculture, the survey provides a broader picture of butterfly health across the country, rather than in hotspots such as nature reserves or gardens.

Dr Zoe Randle from Butterfly Conservation, who co-ordinated the survey, said the results were some of the best ever recorded for common and widespread species.

The small tortoiseshell, which had been a cause for concern in previous years, had a dramatic turnaround.

Mirroring their resurgence in garden surveys, small tortoiseshells were seen in 80% of the wider countryside sites, compared with just 40% in 2012.

Start Quote

We're at the mercy of the weather to be honest”

End Quote Dr Zoe Randle Butterfly Conservation

Both the large and small 'cabbage' whites, common blue, small copper and brimstone all thrived too but the most abundant was the meadow brown, with 8,000 more butterflies counted this year than last year.

"[Farmland] provides nectar sources for butterflies," explained Dr Randle.

"It also provides caterpillar food sites, so the immature stages have got something to eat.

"There are hedgerows and trees that provide places to lay their eggs and to stay out of the elements."

Although warm weather provides perfect conditions for these cold-blooded insects to feed and breed in the summer, mild winters can cause a problem.

"We don't really know with all this extreme rainfall, what effect that's going to have on our butterflies. It's unprecedented so there's no scientific evidence to show one way or another," said Dr Randle.

"One thing we do know is that warm, wet winters are no good for some species of moth."

Meadow brown with dew The meadow brown was the most abundant species in the survey

"These mild winters increase pathogen activity, so there will be lots more fungi about," she said, explaining that butterflies which overwinter as eggs or caterpillars are vulnerable to diseases caused by fungi.

According to Dr Randle, warm days in winter can also cause butterflies to emerge early when fewer food plants are available.

This can result in the insects running out of energy before the breeding season, which leads to population declines.

"We're at the mercy of the weather to be honest," said Dr Randle.

"In the longer term, species are generally declining, and one good summer doesn't ensure it's going to be good in the future."

She added that this year's survey is vital in determining the impact of mild, wet winter conditions for the summer-loving species.

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