Usually one generation is produced each year. Females lay eggs in groups underneath nettle leaves during May, after around two weeks the eggs hatch. The caterpillars live in groups, protected by a web of silk, before dispersing to pupate, hanging underneath vegetation (3). The adults emerge around two weeks later, in late July. They gather together at sources of nectar, building up reserves to see them through hibernation, which usually begins in September (2) and occurs in hollow trees and other refuges, including attics (4). They do not mate until the following year, emerging from hibernation as early as February, with peak emergence occurring in April. Males defend territories in sunny locations, and chase any females that pass by (2).