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The brown hairstreak (Thecla betulae) is a butterfly in the family Lycaenidae, with a range spanning most of the Palearctic. It is difficult to observe, spending most of its time in groups in the tops of trees (often tall European ashes on the edge of woodland, known as "master trees"), where they feed on the honeydew of aphids. The females come down to lower levels to lay their eggs on blackthorn twigs, and can sometimes be seen feeding on nectar from flowers such as hemp-agrimony, common fleabane, yarrow and bramble. The species is on the wing in late summer and early autumn; the eggs overwinter and hatch in the spring when the blackthorn buds burst. This brown hairstreak was photographed in Rila National Park, Bulgaria.Photograph credit: Charles J. Sharp