Purple Hairstreak

Favonius quercus is a small oak-associated butterfly in the hairstreak subfamily, Theclinae. [2]

Males have extensive purple upperwing colour; females retain a smaller purple forewing patch against dark ground colour. Both sexes have silvery-grey undersides crossed by a narrow pale line, an orange hindwing eyespot and short tails. British adults span approximately 30–40 mm. [1]

The species occurs across much of Europe and extends into western Asia. Oaks in woods, parkland, hedgerows and avenues can support colonies; sunny crowns are particularly important adult habitat. [2]

Eggs are deposited beside oak buds during summer. The caterpillar develops within the egg and remains there over winter, emerging as the buds open in spring. Mature larvae pupate in sheltered litter or bark. [1][2]

British caterpillars eat oak buds and young foliage, especially English and sessile oak. Adults obtain much of their food from aphid honeydew, occasionally descending to flowers such as bramble. [1]

Adults are especially active around the canopy on warm summer evenings. Dutch observations place the main flight in July and August, in a single generation. Individuals occasionally descend in the morning to drink moisture. [2]

The short, brown larva has pale oblique markings and fine hairs. Its colouring matches the buds and bark among which it rests by day; feeding occurs mainly at night. [1]

The epithet quercus refers to oak, the plant around which the species' life cycle is organised. Linnaeus named the species in 1758. [2]