The butterfly hibernates over winter before laying its eggs in early spring, in batches of up to 400 at a time. The eggs are ribbed, olive green, and laid on the upper parts and the undersides of leaves of nettle plants and hops. The caterpillars, which are shiny black with six rows of barbed spikes and a series of white dots on each segment, and which have a shiny black head, hatch after about a week. The chrysalis may be either grey, brown, or green in colour and may have a blackish tinge. The caterpillars grow up to 42 mm in length.