- Name also: European Peacock
- Latin synonym: Inachis io, Nymphalis io
- Family: Brushfooted Butterflies – Nymphalidae
- Subfamily: True Brushfoots – Nymphalinae
- Wing span: Medium-sized–large, 45–65 mm (1.8–2.6 in.). Females larger than males.
- Wing upper side: Rust red, with large black-edged and shiny blue eye-blotches.
- Wing underside: Forewing from brown to black, upper surface eye-blotch faintly discernable also on underside. Hind wing almost black with unclear band and stripes.
- Habitat: Meadows and grazing land as well as open forests and gardens.
- Flying time: From May–mid-June, then late July–September.
- Overwintering form: Adult butterfly.
- Larval foodplant: Nettle (Urtica dioica) and also hop (Humulus lupulus). Caterpillar is a monofag (specialised in one source of nutrition).
The (European) Peacock was previously rare but in recent years it has become one of the most common and easy-to-recognise butterflies, at least in the south of Finland. The northern limit of its habitat as a common species is around Vaasa–Kuopio line but the peacock can be seen also in Lapland occasionally. The species’ best and most reliable markers are the large eye blotches on the upper surface of both the forewings and hind wings.
Males wait for females on rocks and in forest margins, where they defend their territory. The females lay their eggs in clusters on the underside of nettle leaves. The caterpillars colonise the host plant together and make cocoons in the stalks and e.g. on the walls of buildings.