Thanks to an army of passionate lepidopterists, butterflies are currently the UK’s best-studied insects. A pair of citizen science projects – the UK Butterfly Monitoring Scheme and Butterflies for the New Millennium – have respectively been measuring butterfly species abundance (how numerous they are, involving tens of thousands of volunteers conducting surveys in more than 2,000 specific sites) and occurrence (how widespread they are, using information of any known sightings to track distribution) across the country for years. Nevertheless, even such close observation hasn’t been able to prevent an overall 76 per cent decline in either the abundance or occurrence (or both) of the UK’s resident and regular migrant butterflies over the past four decades according to the latest ‘State of the UK’s Butterflies 2015’ report by Butterfly Conservation and the Centre for Ecology & Hydrology.
‘Overall the situation is stark,’ says Richard Fox, Head of Recording at the Conservation and lead author of the report. ‘Most butterflies have decreased since the 1970s and an alarming number of common species have declined severely.’ Persistent habitat destruction, through the intensification of agriculture and changes to woodland management, are believed to be the leading cause for why so many species are significantly dropping in number. Even previously abundant species, such as the gatekeeper and the wall brown, have respectively seen 41 per cent and 87 per cent declines in abundance since 1976. Other species, including the Essex skipper, white admiral and marsh fritillary all show signs of serious decline in numbers, despite some expanding their ranges.
“We think conservation has made a huge impact for those threatened species whose trends seem to be slowly coming around”
‘On the other hand,’ continues Fox, ‘trends over the past decade provide grounds for optimism and show that our approach to conserving threatened butterflies can stem and even reverse declines.’ He refers to data that shows how some resident species have been growing in number in the past decade, with the pearl-bordered fritillary and the Duke of Burgundy increasing in abundance by 45 per cent and 67 per cent respectively, and the dingy skipper and silver-studded blue increasing in occurrence by 21 per cent and 19 per cent respectively.
‘We think conservation has made a huge impact for those threatened species whose trends seem to be slowly coming around,’ he adds, ‘but our next project from a data point of view is to see if we can actually prove that. I’m pretty confident that there is a link there.’
Additionally, several migrant species are arriving in ever-greater numbers, and even staying long enough to be considered resident species. These include the clouded yellow, the red admiral and the painted lady, whose numbers have all increased since the 1970s.
This article was published in the February 2016 edition of Geographical magazine.