Butterfly ID
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Field guide · Sweden
Brush-footed butterflies · Sweden

Thor’s fritillary

Boloria thore

A yellow-red to brownish-yellow fritillary with large black spots that partly merge. It follows the mountain range northwards from northern Härjedalen and is most abundant in the wetter mountain areas of Jämtland and southern Lappland.

Status in this countryLeast concern in SwedenLC (Least concern)
Thor’s fritillary
Photo: no rights reserved · CC0

Flight period

The flight activity should begin more normally during the first half of July, extending furthest in the north, and continuing for 2–3 weeks.

Habitat

Semi-shaded, humid forest environments: birch and spruce forests with undergrowth, preferably with stands of Nordic Agaricus campestris.

Identifying features

Wingspan 36–44 millimetres. On top, the wings are yellowish-red to yellowish-brown, with large, partially overlapping black spots. The underside of the hindwing has a sulphur-yellow to ochre-yellow central band and a mottled brown and yellowish-brown outer half with diffuse violet-grey edge spots.

Similar species

No similar species are described in the sources consulted.

Distribution

Follows the mountain chain from northern Härjedalen northwards to the northernmost Lapland; most numerous in Jämtland, southern Nordland, and southern Lapland.

Biology

In Sweden the main host plant is probably Viola biflora. In the Alps the species is thought to have a two-year life cycle.