Seven new butterflies recorded at National Trust site in ten years

19/05/2006 00:00:00 August 2007. The limestone hills around the National Trust’s Arnside Knott and Silverdale properties on the Lancashire/Cumbria border have been witnessing a remarkable butterfly ‘invasion’. In less than a decade, no less than seven species of butterfly new to the area have begun colonising the sites, as climate change and changing habitat affect their traditional distribution. One of the best known areas for butterflies in the country, more than half of all the species of butterfly in the UK can now be found in this area. There are now 34 species of butterfly found at Arnside Knott and Silverdale. The area is ecologically very rich and forms the southern range limit of many northern species, and the northern limit of many southern species. This makes it a particularly important area for studying the impact of climate change on plants and animals. Butterflies are hyper-sensitive to changes in weather and represent a valuable thermometer to our understanding of how our climate is changing.

The seven species of butterflies that have colonised Arnside Knott and Silverdale in the last decade are the Speckled Wood, Gatekeeper, Ringlet, Comma, Silver-washed Fritillary, White-letter Hairstreak, and Small Skipper. The Small Skipper and Ringlet are the most recent butterflies to arrive on National Trust land, with the first sightings this year. Five of the seven are widespread southern species but the Silver-washed Fritillary and White-letter Hairstreak are local woodland specialists. Records from Butterfly Conservation show that many of these butterflies have been moving north in recent years. It is highly likely that climate change is the main reason for this welcome expansion, perhaps especially, the arrival of milder winters. Habitat management by conservation organisations active in the area including the National Trust, Butterfly Conservation, the RSPB and Natural England have also helped to create conditions which are likely to attract these butterflies. Management includes the restoration of limestone grassland, scrub clearance, traditional coppicing of woodland and grazing by sheep and cattle.

Matthew Oates, National Trust Nature Conservation Adviser and leading butterfly specialist, who conducted detailed surveys of butterflies in the area twenty five years ago, says, ‘The influx of seven new butterflies into the Arnside and Silverdale area in such a short space of time is remarkable and thought to be unprecedented. These are butterflies being recorded in an area where they have never been seen before. As a result of these new arrivals thirty-four species of butterfly can be found here, making it an even more special area for butterflies.’

Two rare resident species of butterfly, the Duke of Burgundy and the Scotch Argus, are by contrast struggling, despite conservation efforts. Climate change may be a key adverse factor. The thin limestone soils may be becoming too drought prone for Duke of Burgundy caterpillars which feed on cowslips and primrose and need green leaves. Despite excellent habitat management the Scotch Argus is now in worrying decline at Arnside Knott and it may be that the area is becoming too warm for this northern butterfly. The National Trust is working closely with Butterfly Conservation to try and arrest these declines.

Richard Fox, who co-ordinates the national butterfly recording scheme for Butterfly Conservation, said ‘The amazing speed at which these butterflies have moved into the area reflects the pace of change. Despite a wet summer this year, the long-term trend is that species will continue to move and adapt as a result of warmer weather. Our research suggests that while some butterflies are benefiting from current levels of climate change, ‘northern’ species including the Scotch Argus and Northern Brown Argus, which both occur at Arnside Knott, are already declining in Britain as a result of warmer weather. Climate change presents a serious conservation challenge.’