The latest results from the UK Butterfly Monitoring Scheme (UKBMS) suggest the heatwave and drought of summer 2022 has had a negative impact on some UK butterfly species. UKBMS data to be collected in 2023 will give a fuller picture of how butterflies fared in late summer, particularly for species whose caterpillars would be feeding on vegetation at that time.
UKBMS, led by Butterfly Conservation, the UK Centre for Ecology & Hydrology (UKCEH), British Trust for Ornithology (BTO) and the Joint Nature Conservation Committee (JNCC) has monitored the status of UK butterflies for five decades.
Analysis of records collected by volunteers during 2022 show that overall, it was an average year for butterflies, compared to annual abundance data from the past 50 years, though there was a marked difference over the course of the flying season. There were good or average numbers of species who have offspring that emerge into adulthood in spring or early summer, but there was a significant decline among populations of many butterflies that are ‘on the wing’ late summer or autumn.
Scientists believe drought killed off many plants that species rely upon, meaning female butterflies struggled to find anywhere to lay their eggs or there was not enough food for the caterpillars when they hatched. They warn the reduction in some populations could have a knock-on effect this year with noticeably fewer butterflies around.
The impact of the drought was illustrated in the changing fortune of some species that have multiple generations in a year.
Green-veined White, Small White and Small Tortoiseshell appeared in good or average numbers during the spring and early summer, but numbers in the subsequent generation were greatly reduced following the widespread drought conditions. Similarly, while numbers of post-overwintering adults of Peacock and Brimstone were good during the spring and early summer, numbers later in the year were poor.
The Small Tortoiseshell had its fourth worst year since the UKBMS began monitoring butterfly numbers in 1976, and its numbers have now fallen by 80 per cent since then.
While the records showed that 2022 was a good year for some species, including Purple Emperor, Large Blue, Chequered Skipper and Dark Green Fritillary, any impact of the drought will not be known until their next generation emerges this summer.
Dr Marc Botham, Butterfly Ecologist at the UKCEH, who carried out this analysis of almost 600,000 records of butterflies by around 4,000 volunteers, said: “In 2022 we collected data from over 3,000 sites and we are incredibly grateful to the thousands of volunteers who carry out monitoring and maintain this invaluable long-term dataset.
“This enables scientists to measure how butterflies are faring as well as assessing the health of our countryside generally. The UKBMS data are vital in assessing the effectiveness of government policies and progress towards the UK’s biodiversity targets.”
Last year ranked as the 27th out of 47 since the records began. Out of 58 UK butterfly species reported on by the scheme, the abundance of 30 were below average, 27 were above average and one was average.
Data gathered by the UKBMS has shown serious negative impacts of droughts on butterflies in 1976 and 1995. Some species have never recovered their former abundance levels after the 1976 drought, although habitat destruction is likely to be a major factor in their failure to bounce back.
Butterfly Conservation’s Head of Science, Dr Richard Fox, said: “UK butterfly populations fluctuate naturally from year to year, largely due to the weather, but the long-term trends are mainly driven by deterioration of habitats due to inappropriate management and pollution, and climate change. Conservation efforts can make a real difference to local populations and working on threatened species in key landscapes to deliver nature recovery is a priority.”
Nature Minister Trudy Harrison added: “Our beautiful butterflies are at risk from a changing climate and human activity. We have set out clear steps to enable nature’s recovery through our Environmental Improvement Plan and Pollinator Action Plan, which will help us meet our legal target to halt the decline in nature by 2030.
"The impacts of warm and dry weather last year are cause for concern, but it is encouraging that the last decade has seen most species stabilise.”
All the data from for UKBMS 2022 can be accessed at UKBMS.org/official-statistics