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Identity

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

Appearance

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]

Range and habitat

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]

Life cycle

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]

Food and host plants

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]

Behaviour

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]

Remarkable detail

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]