Females can be twice as large as males.
Mating takes place from late morning to early afternoon, and in late afternoon or dusk, females begin laying eggs in large clumps on the underside of oak leaves. Eggs hatch in about 2 weeks and are gregarious when young. Fully-grown caterpillars pupate and overwinter in shallow underground chambers. One brood from June-July. G5 - Demonstrably secure globally, though it may be quite rare in parts of its range, especially at the periphery.