Green Hairstreak

Callophrys rubi is the Green Hairstreak, a small member of Lycaenidae. [1]

The green underside carries a fine, sometimes interrupted pale line. British adults measure about 26–33 mm across the wings. Larvae are green with yellow markings and fine hairs. [1]

In Britain, the species occupies heathland, moorland, grassland and woodland clearings. It is widespread but often concentrated around suitable scrub and food plants. [1]

Females lay single eggs. Larvae mature during summer and pupate at ground level; the pupae pass the winter in litter before adults emerge the following spring. [1]

British larval hosts include rock-rose, bird's-foot-trefoil, bilberry, bramble, broom and gorse. This range of food plants permits breeding in several contrasting habitats. [1]

Males defend perching positions during the spring flight season. Settled adults keep their wings closed, exposing the green underside. [1]

The green scales contain repeating three-dimensional networks of chitin and air known as single-gyroid photonic crystals. These structures selectively reflect visible wavelengths rather than producing green through pigment alone. [2]

Microscopy and optical measurements in 2017 showed how differently oriented crystal domains combine to produce a comparatively uniform green appearance. Individual domains can reflect different colours, while their collective response suppresses much of the strong angle-dependent flashing typical of iridescence. [2]