- Family: Swallowtail Butterflies – Papilionidae
- Subfamily: Snow Apollos – Parnassiinae
- Wing span: Large, 55–70 mm (2.17–2.76 in.). Females larger than males.
- Wing upper side: White, forewing with two black blotches. Tip of forewing transparent.
- Wing underside: Like upper surface.
- Habitat: Rich meadows and occasionally on grazing land with trees and bushes.
- Flying time: Early June–early August.
- Overwintering form: Egg, or small caterpillar.
- Larval foodplant: Solid-tubered corydalis (Corydalis solida). Caterpillar is a monofag (specialised in one source of nutrition).
- Endangerment: Endangered, protected in all of Finland, including the Åland Islands.
The clouded Apollo is quite large and easy to differentiate from apollos because it lacks the red ring pattern on its hind wing that is characteristic of the latter. Females of the species can be identified by the bronze-coloured collar around their heads. The best places to look for it are in the Åland Islands and around the south-west of the country.
Males fly around looking for females. Copulated females have at the back of their bodies, a shell-like structure called a sfragis. The male creates it during copulation, and it is assumed that it makes it difficult for the female to copulate again. Solid-tubered corydalis, which the larvae like to feed on, flowers early in the spring and has withered before the butterflies’ flying time. The females are able to find the roots, however, and lay their eggs one at a time close to the ground.