Orchard Ermine Yponomeuta padella
Wingspan 19-22 mm.
Part of a species complex which is still undergoing scientific research, it is very difficult to separate this from similar species, even by genitalia examination, and the best guide is often the foodplant.
The larvae feed on blackthorn (Prunus spinosa), hawthorn (Crataegus) and cherry (Prunus spp), and like its relatives lives gregariously in a silken web.
It is fairly common over most of the British Isles, and flies in July and August, when it is attracted to light.