Oak Eggar

• The males fly in full sun, with an erratic and very fast flight, tracking the pheromone of the females, which by contrast are nocturnal and barely move.
• Its caterpillar, large and very hairy, can take two years to complete its development in mountain populations, overwintering twice.
• The caterpillar's hairs are irritant and cause a rash on contact.
• Its name misleads: despite being named after the oak, the caterpillar feeds mostly on heather and bramble, and heathland populations do not depend on oak at all.
• Sexual dimorphism is marked: the male is reddish brown and flies by day at great speed, seeking females by scent, while the female is larger, paler and flies at night.
• Watching the males patrol in zigzags over the heather moors in broad daylight is a characteristic scene of the European summer, and it puzzles anyone who expects a moth to be nocturnal.
• In the north of its range the cycle takes two years: the caterpillar overwinters twice before pupating.
• The caterpillar is large and very hairy, with hairs that can cause irritation.

Skeleton type

Invertebrate - chitin exoskeleton (insect)

Habitat and environment

Heathland, scrub, moorland and woodland edges of Europe

Size at birth

The caterpillar reaches about 65 mm when fully grown and is covered in dense hairs

Sexual maturity

The adult emerges with reduced mouthparts and does not feed; the cocoon is acorn-shaped, which is where the scientific name quercus comes from (it does not eat oak)

Gestation / incubation

In the south of its range the cycle is completed in one year; at more northerly latitudes it takes two, with the caterpillar overwintering the first year and the chrysalis the second

Litter / clutch size

The eggs are released loosely among low vegetation, without being fixed to the plant; an unmated female can attract a large number of males

Sources consulted: Butterfly Conservation (Reino Unido) · Lepiforum · Speybroeck et al · Ficha de especie de Lasiocampa quercus · NatureSpot · UKmoths, ficha Oak Eggar

Best time: On the wing for about two months between May and September depending on latitude: July and August in the southern lowlands, and from late May to early July further north. The males fly by day, above all in full sun, and the females at dusk