The White-Letter Hairstreak Butterfly (Strymoidia w-album) is identified by the distinctive W mark on the underside of the wings; it also has a pair of black tails with white ends at the rear of the wings.
It is associated with woodland containing its food plant, the elm tree. The species declined after the caterpillars food plant was reduced following Dutch elm disease in the 1970s.
They spend most of the time in the tree canopy feeding on aphid honeydew, the food for the adults. They are occasionally seen nectaring on the ground flora, making them easier to spot. They are one of three butterflies that can be seen walking on leaves opening and closing their wings.