Butterflywatch: UV torches aid monitoring of rare and elusive species

Nature lovers have been enjoying using UV torches to discover the vivid fluorescent colours of plants and animals at night for a few years now. Now lepidopterists have realised that UV torches provide a highly effective new way to find and count rare and elusive butterflies. Butterfly Conservation is working with Berks, Bucks & Oxon Wildlife Trust (BBOWT) to train volunteers to hunt for glow-in-the-dark caterpillars.

Elusive tree-dwelling butterflies such as the rare brown hairstreak are particularly difficult to monitor in the wild. The butterfly lives in treetops and is difficult to see as an adult, and its caterpillars are superbly camouflaged. Brown hairstreak colonies are typically monitored by painstakingly hunting for its microscopic eggs, which are found on blackthorn twigs in midwinter.



But now there’s an easier way: shining a UV torch on hedgerows at night can reveal glowing caterpillars . UV torches make the luminous larvae gleam as if they are producing their own light – an effect known as photoluminescence. The well-camouflaged chrysalis of the purple emperor is virtually impossible to find in daylight and yet it also glows under UV light – delighting enthusiasts who search for these charismatic insects.

Sign up to Down to Earth The planet's most important stories. Get all the week's environment news - the good, the bad and the essential after newsletter promotion Steven Lofting, a conservation manager for Butterfly Conservation , says surveying via UV torches could be “a gamechanger” and significantly improve our understanding of rare and hard-to-find butterflies’ distribution, abundance and ecology..