Green Hairstreak

The green underside

The green hairstreak is the only British butterfly with a green underside on both wings. The colour is structural — produced by the microscopic arrangement of wing scale cells — rather than a pigment green, which gives it a slightly iridescent quality. A thin white streak (the “hairstreak” of the name) runs across the underside of both wings, though in this species it is often reduced to a row of small white dots.

Territorial males

Male green hairstreaks are strongly territorial, selecting a prominent perch — often the top of a gorse bush or hawthorn spray — and launching spiralling aerial pursuits to chase away rival males. They return repeatedly to the same perch after each encounter. This behaviour makes them relatively easy to observe in spring. Females are more secretive, moving quietly through the vegetation to find egg-laying sites.

Larval foodplant flexibility

Unusually for a hairstreak, the green hairstreak uses a wide variety of larval foodplants depending on habitat. On heathland it favours gorse and bilberry; on chalk downland it uses rock-rose and bird’s-foot trefoil; in scrub it may use dogwood or bramble. Eggs are laid on flower buds, and the larvae feed primarily on flowers and developing seeds rather than leaves. This flexibility makes it one of the more widespread and adaptable of the British hairstreaks.

Camouflage strategy

The dull brown upperwing is exposed only in brief glimpses — when the butterfly lands, it immediately closes its wings to show the green underside. Against grass, lichen, or young leaves this camouflage is highly effective. The green hairstreak almost never basks with open wings; the combination of cryptic upper and lower surfaces gives it two separate camouflage strategies depending on behaviour.