Brown Hairstreak (Thecla betulae)
The beauty of betulae ...
T. betulae is the largest Hairstreak to be found in the British Isles. It is a local species that exists in self-contained colonies that breed in the same area season after season. Despite this, it can prove extremely elusive, since it spends much of its time resting and basking high up in tall trees and shrubs.
Adults emerge in the morning with males generally appearing a few days before females. This is a warmth-loving butterfly and is rarely seen on overcast days. On sunny days the adults will rest with wings open, absorbing the sun's rays on their dark brown wings, which gradually close as they warm up. In flight, the adults are easily mistaken for the Gatekeeper (Pyronia tithonus), which flies at the same time. The day flying male Vapourer moth (Orgyia antiqua), though somewhat smaller than T. betulae, is also often mistaken for betulae by some observers.
The males are the more elusive of the two sexes, congregating high on ash ‘master trees’ that are positioned around the breeding area, where they feed on aphid honeydew. They occasionally come down to feed on various nectar sources, probably when honeydew is scarce. When they do come down they can be remarkably tame and easy to observe. This is one of the latest species to emerge in the British Isles, with adults first seen on the wing in late July or early August. There is one generation each year. Two separate females are illustrated above.