Upperside is purple-black with a wide, bright yellow border on outer margins, and a row of iridescent blue spots at the inner edge of the border. Overwintered adults mate in the spring, the males perching in sunny openings during the afternoon to wait for receptive females. Eggs are laid in groups circling twigs of the host plant. Caterpillars live in a communal web and feed together on young leaves, then pupate and emerge as adults in June or July. After feeding briefly, the adults estivate until fall, when they re-emerge to feed and store energy for hibernation.
Some adults migrate south in the fall.
Usually one flight from June-July. Older caterpillars wander about and may be found on plants that they do not eat. They walk down the trunk to the sap and feed head downward. They will also feed on rotting fruit, and only occasionally on flower nectar. Adults live 10-11 months and may be our longest lived butterfly.