The small, fast-flying Chequered Skipper, which became extinct in England in 1976, now only occurs in the UK within a 30-mile radius of Fort William in the Highlands.
The butterfly’s restricted distribution can be explained by the region’s warm, damp summers and mild winters which allows the deciduous Purple Moor-grass, on which the caterpillar feeds, to stay green late into the autumn.
This helps the caterpillars to complete their development before hibernating for the winter. Elsewhere in the UK, Purple Moor-grass turns brown too early in the year for this to happen.
Recent work by Butterfly Conservation and the JNCC (Joint Nature Conservation Committee) has predicted, through computer modelling, that the butterfly’s distribution could be underestimated by around 20% at a 10km level and as much as 80% at a finer 1km resolution.
In 2012 and 2013 Butterfly Conservation Scotland encouraged the public to look for the butterfly in the top 100 1km squares that the modelling predicted were the most suitable for the butterfly, but where it had not previously been recorded.
Over the two years the butterfly was found in 20 of the targeted squares but not in 27, the remaining squares were not surveyed. But Chequered Skipper was also found in an additional 48 new 1km squares, where it had not previously been recorded. These discoveries have increased the known range of the butterfly by a staggering 28% at a 1km resolution.
Most new sightings were within the species known range in north Argyll and south Lochaber, but there are a number of hotspots of new sightings including the far west end of Loch Arkaig, Glen Etive, around Acharacle, Loch Leven, Taynault area and the Ardnamurchan peninsula.
The results also gave an insight into how elusive the butterfly can be as Chequered Skipper was not always seen on repeat visit to squares that were surveyed more than once. In many cases it took three visits to confirm the butterfly’s presence. We are therefore planning to repeat the survey again in 2014.
The results were unveiled at Butterfly Conservation Scotland’s annual Spring Recorders Gathering, attended by almost one hundred active volunteers at Scottish Natural Heritage’s Battleby Conference Centre.
Dr Tom Prescott, Senior Conservation Officer for Butterfly Conservation Scotland, said: “The survey has been a marvellous success and shows what can be achieved by encouraging the public to target survey effort to specific squares.
“It has also proved the worth of the model and that such an approach may be a useful technique to help determine the true distribution of other under-recorded species in Scotland.”
The Chequered Skipper is usually on the wing from mid May until the end of June. It can be seen on warm and sunny days, even during brief spells of sunshine, feeding on nectar particularly bugle, marsh thistle and orchids