Two declining butterflies suffered their worst year on record in 2017 after hopes of a butterfly revival were dashed by a chilly snap in spring and a gloomy, wet summer, a study has revealed.

Grayling and Grizzled Skipper recorded their lowest numbers since records began as difficult weather conditions caused problems for some of the UK’s species.

There had been hopes that UK butterflies would bounce back after the summer of 2016, the fourth worst on record.

And although butterfly numbers last year were up on 2016, they were still way below average with 2017 being the seventh worst year on record, the annual UK Butterfly Monitoring Scheme (UKBMS) revealed.

Grizzled Skipper and Grayling had their worst year on record for the second year running. Grizzled Skipper was down 9% compared to 2016 and the population has now more than halved since the 1970s. Grayling declined by 6% compared to 2016, its numbers have shrunk by 63% over the last decade.

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Grayling by Patrick Clement, Butterfly Conservation

Grayling declined by 6% compared to 2016; its numbers have shrunk by 63% over the last decade.

The threatened Dingy Skipper saw numbers fall by 22% compared to 2016 and the rare Marsh Fritillary experienced a decline of 12% over the same period.

It wasn’t just rare species that struggled. The Large White, one of the UK’s most well-known and widespread butterflies, saw its numbers tumble by 19%. This common butterfly is now also in a state of long-term decline.

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Video footage coutesy of David Breiter via Creative Commons

There had been hopes for a good butterfly year as many spring species emerged earlier than usual following a warm start to 2017. Butterflies need warm, dry weather during their flight periods in order to feed and mate.

But a cold snap at the end of April saw other spring species such as the Grizzled Skipper and Duke of Burgundy struggle.

The second half of the summer was cloudier and wetter than average which caused further problems for species already struggling from a combination of habitat loss and climate change.

The other two common white butterflies also had a poor year. Small White was down 16% and Green-veined White down 2%.

Many species did enjoy a better year than 2016.The widespread Red Admiral was up 78% and Comma numbers rose by 91% compared to 2016. Both species are increasing over the long term.

The warm start to the year helped some spring butterflies such as the threatened Pearl-bordered Fritillary whose numbers rose by 57% compared to 2016. This is a species that has also benefitted from targeted conservation work.

The rare White Admiral bounced back following a terrible 2016 with an annual increase of 157%. Small Copper was up 28% compared to 2016 after a series of poor years and had its best year on record in Northern Ireland.

Professor Tom Brereton, associate director of monitoring at Butterfly Conservation, said: “There is little comfort in these results for the UK’s hard-pressed butterflies.

“2017 was the seventh worst in the 42-year series and makes it five below average years in a row. On the positive side, there is much good conservation work happening across the country, which will aid any recovery should we get a helping hand with the weather.”

The UKBMS is led by Butterfly Conservation, the Centre for Ecology & Hydrology, British Trust for Ornithology and the Joint Nature Conservation Committee.