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Latest Butterfly Official Statistics

News Item 2019

Butterflies bounce back in heatwave summer
2018 Summary of Changes table for the UK

UK butterflies bounced back in 2018 following a string of poor years, thanks in part to year’s heatwave summer, a study has revealed. More than two-thirds of UK butterfly species (39 of 57) were seen in higher numbers than in 2017, with two of the UK’s rarest, the Large Blue and Black Hairstreak, recording their best years since records began.

Blackhairstreak © AllanDrewitt

But despite the upturn, 2018 was still only an average year for the UK’s butterflies. Around two-thirds of species (36 of 57) show an apparent decline since records began 43 years ago with 21 of these showing significant long-term declines, the annual UK Butterfly Monitoring Scheme (UKBMS) led by Butterfly Conservation, the Centre for Ecology & Hydrology (CEH), British Trust for Ornithology (BTO) and Joint Nature Conservation Committee (JNCC) revealed.

Numbers of the threatened Large Blue rose by 58% from 2017 levels and the endangered Black Hairstreak was up by more than 900%. Both species benefited from warm and sunny weather when they were flying in the early summer, whilst the cold spell in February and March may have also helped by improving survival of caterpillars and chrysalises. Brown Argus and Speckled Wood also thrived, recording their third best year on record.

Common white butterflies experienced a good year after a recent run of below-average seasons with Large White annual abundance up 118%, the Small White rising by 155% and the Green-veined White increasing by 63%, again due to warm and sunny weather from April to the end of July. The threatened Duke of Burgundy was up 65%. This butterfly has been the subject of intensive conservation efforts in recent years from Butterfly Conservation and partners, with some of the biggest annual increases seen at conservation sites. The butterfly’s population has stabilised over the last 10 years in the face of a significant long-term decline.

The hot spring and summer weather was not ideal for all species. Some grassland butterflies struggled, not helped by drought conditions drying out caterpillar food plants. The Gatekeeper dropped by 20% from 2017 levels and the Small Skipper and Essex Skipper were down by 24% and 32% respectively. It was also a surprisingly poor year for some garden favourites. The Small Tortoiseshell slumped by 38% compared to the previous year and the Peacock was down 25%, whilst the migratory Red Admiral crashed by 75% after a good year in 2017.

Anna Robinson, Monitoring Ecologist at JNCC said: “Understanding changes in the environment is important in driving conservation action. We are grateful to the thousands of volunteers who submit records to the UKBMS, providing really valuable evidence on the state of butterflies in the UK.”

The UKBMS has run since 1976 and involves thousands of volunteers collecting data through the summer. Last year a record 2,873 sites were monitored across the UK. The scheme is organised and funded by Butterfly Conservation, the Centre for Ecology & Hydrology, the British Trust for Ornithology and the Joint Nature Conservation Committee.

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