Large Blue_Photo: Keith Warmington

The Large Blue was pronounced extinct in Britain in 1979 and subsequently reintroduced into this country by Natural England and UKCEH

The UK’s butterflies had a ‘good’ year in 2020 but populations of many species remain in long-term decline, according to the latest annual results.

Trends based on records collected by volunteers have been published by the UK Butterfly Monitoring Scheme (UKBMS), which is led by Butterfly Conservation, the UK Centre for Ecology & Hydrology (UKCEH), British Trust for Ornithology (BTO) and Joint Nature Conservation Committee (JNCC).

Analysis of the abundance data shows that 2020 was the third good year in a row for the UK’s butterflies overall, ranking it 10th best, averaged across all species, since UKBMS began in 1976. However, the fortunes for individual species was mixed. Of the 58 species reported on by the scheme, 31 fared better than their long-term average and 27 species worse.

Dr Marc Botham, Butterfly Ecologist at the UK Centre for Ecology & Hydrology, says: “Despite 2020 being a challenging year for data gathering and conservation activity, we received nearly half a million records from more than 2,500 sites over the year.

“We are incredibly grateful to the thousands of volunteers who were able to carry out COVID-safe monitoring and maintain this invaluable long-term dataset. This enables scientists to better assess how butterflies are faring as well as the health of our countryside generally.”

We are incredibly grateful to the thousands of volunteers who maintain this invaluable long-term dataset - Dr Marc Botham

As numbers decline in the long term, perceptions of what makes a ‘good year’ for butterflies have changed, according to scientists.

Dr Richard Fox, Associate Director of Recording and Monitoring at Butterfly Conservation, says: “Perhaps because of the warm sunny spring weather last year and the fact that more people were enjoying nature as part of their day-to-day activities than ever before, butterflies seemed more numerous.

“We need to be wary of shifting baseline syndrome, whereby we forget (or never experienced) the greater biodiversity that occurred in the UK in former decades and therefore lower our expectations and aspirations for conservation. Here, the UKBMS has a vital role to play in showing how insect populations have declined over time.

“It is worrying that, even after three good years, population levels of so many butterfly species continue to be down compared to 40 years ago.”

Butterfly populations fluctuate naturally from year to year, but the long-term trends of UK butterflies are mainly driven by human activity, particularly the destruction of habitats and climate change.

However, conservation can make a difference to local populations and 2020 was a good year for a number of scarce species including the Large Blue, which had its joint second best year since UKBMS started. The species was pronounced extinct in Britain in 1979 and subsequently reintroduced into this country by Natural England and UKCEH.

Among the UK’s widespread butterfly species, Brimstone, Orange-tip and Marbled White all had a good year, although their numbers were not at the exceptional levels seen in 2019. After a run of four very poor years, numbers of Small Tortoiseshell improved, showing an increase of 103 per cent over 2019 but remaining below long-term average levels and the species still shows a serious (79 per cent) decrease in abundance since 1976.

Small Pearl-bordered Fritillary has now had nine consecutive years with below average numbers, and its populations have declined by 68 per cent since 1976. Painted Lady, a migrant species, also had a poor year and populations of Wall, Grayling and Small Skipper all remained at a low ebb.

All the data from for 2020 can be accessed at UKBMS.org/official-statistics

UKBMS 2020 tables