Butterflies of Scotland
- Purple Hairstreak (Favonius quercus)

Graphics via Wikimedia

Often seen fluttering around high up in oak trees on warm sunny July and early August days. Males have a glossy purple sheen on the upperside, females have two patches on the forewing only. The underside is light grey with a white streak, edged in black, running down the middle of both wings. The hindwings have a short tail with two orange spots at the base on the underside. It is common and widespread across southern and central England and Wales, becoming rarer and more isolated in the north as far as central Scotland. Males tend to stay high up in trees; females come down to lower levels to lay eggs. Both sexes feed mainly on honeydew although females are occasionally attracted to flowers whilst taking a break from egg laying.

Eggs are laid singly at the base of oak buds in late summer ready to hatch the following spring as the buds break. Both Sessile Oak Quercus petraea and Pendunculate Oak Quercus robur, Britain's two native oaks are used and also some introduced species such as Turkey Oak Quercus cerris and Evergreen oak Quercus ilex. In winter the eggs are easily found on close examination of bare branches. The caterpillar is fully developed inside the egg after two or three weeks but doesn't hatch until the spring whereupon it burrows into the flower buds to feed safely concealed. As it gets larger and the buds open it spins a silken retreat and feeds only at night. The caterpillar is dark red-brown and has a darker brown line along its back and paler oblique line along each side. It is very difficult to find due to its resemblance with a brown leaf-flower bud. Pupation usually takes place in the leaf litter where it is tended by ants who bury them, but also sometimes in a crevice in the bark of the foodplant. There is one brood a year with adults on the wing in July and August.

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