There is usually one brood (late July to early September) which hibernates and re-appears the following March to May, with a few stragglers still flying into early July. However it is recorded in every month of the year due to hibernating individuals waking up in winter as a result of disturbance or warmer weather.
Springtime males can often be seen spiralling high in the air in territorial arguments. A male may suddenly leave a territory to follow a female across the countryside until she chooses a roosting site (probably high in a tree), where mating takes place, under cover of darkness and unseen (and as far as we know un-photographed!).
Once mated, females continue journeying, trying hard to shake off any pursuing males. Clusters of 300 to 500 eggs are laid on the undersides of nettle leaves, usually around the middle of the day. Greenish-grey larvae hatch one to three weeks later and develop through five instars into conspicuous hairy black larvae, speckled with white dots, in June and July. They feed inside communal webs, periodically re-built on fresh nettle stems.
Larvae usually pupate on nearby shrubs or tree trunks and the pupae are well hidden, hanging from silk pads for two to four weeks before hatching. Summer emergence in Yorkshire is typically between late 20 July and 8 August, depending on weather conditions and butterflies sometimes hibernate after only a few days. By late August or early September they become less active as they look for somewhere to hide; e.g., tree holes, sheds, garages or even churches. Roosting or hibernating Peacocks may react to disturbance by flicking their wings to show their eye like pattern. At the same time they can produce a creaking sound by rubbing their wings together and a communal roost reacting together can produce a hissing sound like a snake! The eye patterns not only serve to frighten potential predators, but may also direct any attack at the wings rather than the body. Hence the summer sight of Peacocks with bites out of their wings, but still flying.