Conservation experts are urging homeowners not to mow their lawns over the coming months to help boost butterfly numbers, with more than half of UK species now in long-term decline.
Last year was one of the worst on record for butterflies, with 51 of the UK's 59 butterfly species showing a decline in numbers compared with figures for 2023.
The fall is being driven by human activity, the use of pesticides and climate change, experts have said.
The UK Butterfly Monitoring Scheme, run by a coalition of conservation organisations, said renowned butterfly species including the small tortoiseshell, the chalk hill blue and small copper suffered their worst year ever.
It was also the second-worst year, since monitoring started in 1976, for popular butterflies living in gardens, parks and the countryside such as the common blue, gatekeeper and large whites.
Richard Fox, from Butterfly Conservation, said: "I am devastated by the decline of our beloved British butterflies, and I'm sorry to say it has been brought about by human actions.
"We have destroyed wildlife habitats, polluted the environment, used pesticides on an industrial scale and we are changing the climate.
"That means that when we have poor weather, these already-depleted butterfly populations are highly vulnerable and can't bounce back like they once did - and with climate change, that unusual weather is becoming more and more usual."
'Significant' declines in some species
Data revealed 31 species have shown a long-term decline.
Experts said this included 22 species showing significant declines, including widespread butterflies such as the small tortoiseshell, whose numbers have plummeted by 86% since 1976.
The green-veined white has seen a 28% decline, while the grizzled skipper, small pearl-bordered fritillary and chalk hill blue had their worst year on record.
Conservationists said those species required specific habitat to survive, which had been destroyed over the past century.
Dr Marc Botham, butterfly ecologist at the UK Centre for Ecology and Hydrology, said the results were "deeply concerning", particularly as "they can tell us about the health of the wider environment".
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What can be done to help butterflies?
The results come after Butterfly Conservation declared a UK-wide "butterfly emergency" following the worst-ever results of its Big Butterfly Count last year.
Dr Fox said the "best thing we can do" was to create "more habitat".
He said research showed letting part of a garden grow wild with long grass increases butterflies.
"That is why we are calling on people and councils across the UK to pledge to not cut their grass this year from April to September, this simple act can make a real, immediate difference to butterflies, moths and other wildlife," he added.
(c) Sky News 2025: Britons urged to stop mowing lawns to boost butterfly numbers 'in long-term decline'
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