Disa Alpine (Erebia disa) (Thunberg, 1791)
Diagnosis: The forewing upperside is dark brown, with three to five orange-ringed black spots, above and below. The hindwing above is unmarked; below, it is divided into thirds with the middle third the darkest; there are two small light grey spots, one in the centre and the other at the front edge of the wing. Wingspan: 34 to 45 mm.
Subspecies: There are two in North America and more, including the nominate subspecies, in the Old World. Subspecies steckeri, with the basal third of the hindwing underside very pale, creating a banded appearance, flies from the Northwest Territories / Yukon border west through Yukon to Alaska, and subspecies subarctica, with the basal third of the hindwing underside only slightly paler, flies from the Mackenzie Delta east along the arctic coast.
Range: Erebia disa occurs in tundra from northern Scandinavia across northern Eurasia, and in North America, along the arctic coast of Alaska and Yukon to Bathurst Inlet in Nunavut.
Similar Species: Ross's Alpine and Four-dotted Alpines (E. rossii and E. youngi) lack the light grey spots on the hindwing underside; the Taiga Alpine (E. mancinus) lacks the banded appearance beneath and has a reddish-orange flush in the centre of the forewing above and below. [compare images]
Early Stages: The early stages are still unknown, but larvae presumably feed on grasses or sedges.
Abundance: The Disa Alpine occurs in mostly inaccessible areas of the north but is common in this area.
Flight Season: It is on the wing from mid-June to mid-July.
Habits: This species flies in wet boggy tundra.
Remarks: Until recently the next species, Taiga Alpine (E. mancinus), was classified as a subspecies of disa, although its appearance is quite distinct. We found that there are several distinct differences in the genitalia between disa (both the North American and Eurasian subspecies) and mancinus. For example, the triangular process that projects anteriorly from the bottom of the genitalia (the saccus) is a blunt triangle in disa, only slightly longer than its basal width, but it is a long, narrow, spinelike process in mancinus, 3-4 times as long as wide.
© 2002. This material is reproduced with permission from The Butterflies of Canada by Ross A. Layberry, Peter W. Hall, and J. Donald Lafontaine. University of Toronto Press; 1998. Specimen photos courtesy of John T. Fowler.
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