- Family: Brushfooted Butterflies – Nymphalidae
- Subfamily: True Brushfoots – Nymphalinae
- Wing span: Medium-sized, 40–52 mm (1.57–2.05 in.). Females larger than males.
- Wing upper side: Brick red, leading edge of forewing with row of black and pale yellow blotches, outermost pale blotch white. Trailing edge of forewing with large dark patch, two smaller blotches in the middle of forewing. Basal half of hind wing black. Margins of both wings with row of black-edged blue arcs.
- Wing underside: Pale yellowish brown, with dark design resembling pattern on upper wing. Basal half of hind wing blackish brown, outer part with broad, paler strip. Both wings’ outer margins with dark shiny blue arcs.
- Habitat: Meadows and grazing land, open forests, yards and gardens, usually in a cultural environment.
- Flying time: April–early June (overwintered generation), then mid-July–September (second generation).
- Overwintering form: Adult butterfly.
- Larval foodplant: Stinging nettle (Urtica dioica). Caterpillar is a monofag (specialised in one source of nutrition).
Butterflies can be divided into 3 groups according to how much they wander: wandering butterflies, which travel large distances, those that stay put, and those that have individuals that wander and individuals that don’t. Small tortoiseshell falls into the third group.
The small tortoiseshell overwinters as an adult and is among the first butterflies to emerge in the spring (the common brimstone is usually even earlier). Males wait for females in forest margins, where they defend their territory. The females lay their eggs in clusters on the underside of the leaves of the host plant (usually nettle). The caterpillars colonise the host plant together and often make cocoons in the host plant, although they also use tree trunks, house walls and other vertical surfaces.
The small tortoiseshell is common all over Finland and looks a lot like the large tortoiseshell, the yellow-legged tortoiseshell and the Compton tortoiseshell which all are larger than the small tortoiseshell. Besides size it can be told apart from these, however, by the way that the upper surface of its wings are closer to brick red than orange, and the basal part of its hind wings are black.