Regional Species


White-letter Hairstreak
Satyrium w-album

Photograph by Alan Wagstaff

Regional Species

This is rather an elusive species which was considered something of a rarity but is now known to be widely distributed and reasonably common - although seldom seen. The butterfly must have been severely affected by the loss of most large elm trees due to Dutch Elm Disease in the 1980s and 90s but whether it survived, here and there, on surviving trees and re-growth, or whether it has subsequently re-colonised North Wales from the east is unknown. What is known is that there are once again mature elm trees throughout North Wales and that the butterfly is present in most districts - though it has yet to be recorded from Anglesey or the Lleyn Peninsula. It probably remains true to say that this butterfly is commoner and more easily seen in Flintshire and eastern parts of Denbighshire and Montgomeryshire.

This is a single-brooded species with the adults on the wing throughout July and the first half of August. The butterflies spend most of their time high in the canopies of elm trees (or neighbouring trees of other species such as ash) although occasionally they can be observed nectaring on flowers at ground level. Two species of elm are found in North Wales, Wych Elm (Ulmus glabra) is the commoner in the west but English Elm (Ulmus procera) occurs in lowland areas. Both species can be used as the larval foodplant but whether or not there is any preference is unclear. Eggs are laid on the twigs but do not hatch until the following spring when the trees are coming into flower.

The White-letter Hairstreak is a difficult butterfly to identify but any small dull-looking butterflies seen near elm trees might be this species and would be worth a closer look. As with the Purple Hairstreak, the best way to get a view is usually with a pair of binoculars.

Further information available from the NW Lepidoptera Database, including access to detailed records, maps, flight-time charts and photographs.