Butterflies saw their fortunes improve last summer following their worst year on record in 2012 - but numbers were still below average, a UK-wide study has shown.
Some 46 of the 56 species studied in the UK Butterfly Monitoring Scheme in 2013 saw numbers increase compared with the washout summer of the previous year.
Experts said the warm summer last year allowed butterflies to make the most of conservation measures put in place over the past decade to help them thrive.
Rare species such as the Lulworth skipper, whose numbers were up 162% compared with 2012, and the critically endangered high brown fritillary, which increased by 133%, benefited from conservation work.
Common species also saw a revival, including the small, large and green-veined whites which all bounced back from their worst year on record in 2012 to above average numbers last year.
The warm summer helped garden favourite the small tortoiseshell record its best year in a decade, the scheme which began in 1976 showed, and boosted numbers of migrants such as clouded yellow butterflies from the Continent.
But overall, butterfly numbers were still below average last year.
Populations of rare species such as the Duke of Burgundy had become extinct in some areas in 2012’s very wet summer.
And 2013’s very cold spring hit species such as the endangered pearl-bordered fritillary whose numbers were down more than a fifth (22%) on 2012.
The icy weather also harmed the grizzled skipper, whose numbers fell 45% to record lows in the monitoring scheme led by Butterfly Conservation and the Centre for Ecology and Hydrology (CEH).
Butterflies need a warm spring and summer this year to help them sustain their recovery from 2012’s lows, experts said.
Dr Tom Brereton, head of monitoring at Butterfly Conservation, said last year’s revival was very welcome, but there was a long way to go before butterflies returned to “former glories”.
“After the worst year ever, there was bound to be a bounce-back, and quite a few species made a better recovery than expected, so it’s encouraging.
“But we’re still a long way off - we’re below even average numbers.”
The good weather the UK enjoyed last year allowed butterflies to make the most of work to boost butterfly habitat, he said.
“There has been a lot of good conservation put in place in the last decade, agri-environment schemes and conservation efforts, but we haven’t had the weather for butterflies to be able to respond.
“Then last year good management bore fruit.”
CEH butterfly ecologist Dr Marc Botham said: “Annual changes are largely associated with the weather. However, the data show that a number of species have been significantly declining over the last 38 years.
“This highlights the importance of maintaining long-term monitoring, reliant on the immense dedication of thousands of volunteers, to determine species and habitats of conservation priority.”
The UK Butterfly Monitoring Scheme involves thousands of volunteers collecting data every week throughout the summer from more than 1,000 sites across the UK.