Butterflies across the UK have been hit hard by an unusually cold and wet spring, conservationists have warned.

April was the sunniest ever but it also experienced a record number of frosts followed by the wettest May for England in 54 years. Native butterflies such as the Little Tortoiseshell, Great White and Red Admiral have been badly affected, with numbers down from 10-year averages, according to the Butterfly Conservation charity.

The cold delays the emergence of butterflies and they do not do well in the rain because it hinders their flight. “They’re sort of solar powered,” said Zoë Randle, senior investigator at Butterfly Conservation. “They need the sun to warm their bodies so they have enough energy to fly, eat and find mates.”

It is not clear whether the cold spring delayed the emergence of these species or whether it is symptomatic of a wider decline. Climate degradation increases the likelihood of extreme weather events, and their increased regularity does not give butterflies a chance to recover from year to year. The comma and green-veined white populations also appear to be very low.

“It’s a story of doom,” Randle said. “Many of our large country species are in decline and we really don’t understand why. There will be a cocktail of factors, so it is habitat loss, agricultural intensification, climate change as well as development.

The researchers looked at spring data from the UK butterfly monitoring program and compared it to average counts for 2010-19. They are now urging the public to help scientists build on this data base by participating in the annual UK-wide Big Butterfly Count, the world’s largest survey of butterflies.

The three-week citizen science event is open to anyone across the country and runs from July 16 to August 8. Participants should spend 15 minutes in an outdoor space counting common butterflies and moths they see and recording their findings on the Big Butterfly Count app. Free identification cards or an identification application are available.

A drop in the number of butterflies is often an early warning of a larger ecosystem decline, as the insects respond quickly to changes in the environment. Wildlife TV presenter Chris Packham, who is vice president of Butterfly Conservation, said logging butterflies is a small but crucial contribution that anyone can make.

“Because butterflies and moths are great indicators of the impacts of climate change and other human environmental factors, collecting data on their numbers is really important,” he said. “So something as simple as recording a butterfly spotted in your garden, in your local park, or in your planter can play a role in vital research into a global problem.”

More than 100,000 Citizen Scientists participated in last year’s tally, the highest number on record, but it is worrying that the number of butterflies and moths spotted was the lowest since the start of the project 12 years ago. This could be because the warm spring meant the butterflies came out earlier, potentially ending their life cycle by the time the investigation began on July 17.

About three quarters of UK resident and regular migrant butterflies declined in number or in distribution since the start of surveillance in the 1970s. Although the general picture is one of extirpation, species are also being discovered in new areas, such as the Jersey tiger moth, which was well established along the coast south of England but now appears to be spreading north. This is included in the enumeration of common species for the first time.

There are other successes. The speckled wood butterfly saw a 84% increase in abundance since 1976, and the Red Admiral – who was once a summer migrant – also winters in the UK due to milder weather and is doing relatively well. One of Britain’s rarest butterflies, the Heather Fritillary, was near extinction in the UK, but its numbers are increasing thanks to habitat restoration efforts over the past 20 years.

The launch of the Big Butterfly Count 2021 takes place today at Winchester Science Center.

Number of large butterflies 2020 Top 10

1. Large white (+ 44%)
2. Small white (+ 7%)
3. Goalkeeper (-14%)
4. Peacock (-42%)
5. Meadow brown (-2%)
6. Red Admiral (-33%)
7. Small tortoiseshell (-41%)
8. Common blue (+ 9%)
9. Ring (-18%)
10. Comma (-29%)

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