Mixed year for UK butterflies in 2023

The latest results from the annual UK Butterfly Monitoring Scheme (UKBMS) show that 2023 was a mixed picture for butterflies, with some species soaring while others continued worrying declines.

Half the 58 species had a better than average year while the other half were below average at monitored sites. Species that flourished included Chequered Skipper, Brimstone and Large Blue, which all recorded their best year since the UKBMS began in 1976.

Another species recording its best-ever year was Red Admiral, a migratory species that has begun to overwinter in the UK as the climate has warmed, making it a common visitor across all habitats, including gardens. Its numbers have increased by 318% at monitored sites since 1976.

Brimstone had an excellent year across the UK in 2023 (Ian Curran).

 

Ups and downs

At the other end of the scale were Small Pearl-bordered Fritillary and Small Tortoiseshell, recording their lowest numbers in the 48 years of monitoring, declining by 71% and 82% respectively since 1976. Small Tortoiseshell had its worst year on record in England, second worst in Wales and joint fifth worst in Scotland in 2023, but did really well in Northern Ireland, logging its second-best year.

Large Blue, which was reintroduced to the UK after becoming extinct in the 1970s, recorded its best year yet, showing that conservation work with this species is really working. 

Other species that had a remarkable year included Brown Argus, Marbled White, Comma, Black Hairstreak and Holly Blue, which all ranked in their top three best years since 1976. On the other hand, Cryptic Wood White, Grizzled Skipper, Pearl-bordered Fritillary, Grayling and Scotch Argus faced significant difficulties. 

Green-veined White and Ringlet both had a poor year, perhaps suffering ongoing effects from the drought the previous summer. 

Brown Argus was another species that fared well last year (Ian Curran).

 

Citizen science

The UKBMS, which began in 1976, is one of the world's longest-running insect monitoring schemes. It now records data on more than 3,000 sites per year and the resulting dataset is a crucial resource for understanding changes in insect populations. It has provided significant insights into almost all aspects of butterfly ecology. The scheme is led by Butterfly Conservation, the UK Centre for Ecology and Hydrology (UKCEH), British Trust for Ornithology (BTO) and the Joint Nature Conservation Committee (JNCC).

Dr Richard Fox, Head of Science at Butterfly Conservation, said: "Butterfly numbers fluctuate naturally from year to year, largely due to the weather, but the long-term trends of UK butterflies are mainly driven by human activity, including habitat damage and destruction, pesticide use, pollution and climate change. By monitoring long-term butterfly trends we can learn about the impact of climate change and other factors on our native wildlife."

Dr Marc Botham, Butterfly Ecologist at the UK Centre for Ecology and Hydrology, added: "Butterflies are an indicator species, meaning they can tell us about the health of the wider environment, which makes the UKBMS data invaluable in assessing the health of our countryside and natural world in general. The mixed results this year emphasise the need for continued monitoring and conservation efforts to protect these important species and their habitats."