Butterflies Crash In Fourth Worst Year On Record

12 April 2017

White Letter Hairstreak_John Murray

















UK butterflies suffered their fourth worst year on record in 2016 with the majority of species experiencing a decline in numbers, a study has revealed. A mild winter followed by a cold spring contributed to conditions that saw both rare and widespread species struggle despite many parts of the UK enjoying a warm and dry summer.  Some 40 of the 57 species studied recorded a decline compared with 2015, 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.


The highly threatened Heath Fritillary had its worst year on record for the second year running, while the Grizzled Skipper, Wall, Grayling, White-letter Hairstreak and White Admiral all recorded their worst ever years.  The Heath Fritillary, restricted to just a handful of sites in southern England, saw numbers slump by 27% compared to 2015. This ongoing decline raises fears for the long-term future of the butterfly whose numbers have fallen by 82% in the last decade.


The rare Grizzled Skipper, found in southern England and parts of Wales, saw numbers tumble by 24%. The butterfly is a spring-flying species emerging from April, a month that was around a degree colder than the long-term average in 2016.  The Grizzled Skipper’s struggles mirrored a bad year overall for the skippers with all but one of the UK’s eight species suffering a fall in numbers compared to 2015.


The White Admiral, White-letter Hairstreak and Grayling slumped by 59%, 42% and 27% respectively while more widespread species also struggled with the Wall down 31%, the Gatekeeper down 48% and Meadow Brown falling by 31% compared with 2015.  Research suggests that the UK’s increasingly mild winters are having a negative effect on butterflies as they may lead to increased disease, predation or disruption of overwintering behaviour.


Cold springs can also cause problems for butterflies by reducing or delaying emergence leading to shortened lifespans. Some species bucked the trend to record reasonable years. The previously extinct Large Blue, one of the UK’s rarest butterflies, recorded its second best year on record with numbers up 38% on 2015.


The butterfly has responded to conservation work to improve the specific grassland habitat that it relies upon to thrive and has showed a significantly increasing population trend since its reintroduction in 1983.  The widespread and migratory Red Admiral recorded a rise of 86% compared to 2015 and the Clouded Yellow, another mainly migrant species, saw its numbers rise by 35%. 

Anna Robinson, Monitoring Ecologist at JNCC said: “We are really grateful to the thousands of volunteers who get involved in monitoring the UK’s butterflies.


“The evidence provided by the UKBMS is of great importance in showing the need for conservation action to improve the situation.” 


The UKBMS has run since 1976 and involves thousands of volunteers collecting data through the summer. Last year a record 2,507 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.


2016 Summary of Changes table for the UK.

Full UKBMS Press Release