Sooty Hairstreak
Satyrium fuliginosum (W.H. Edwards, 1861)

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Diagnosis: The small (wingspan: 24 to 30 mm), rounded wings of this drab species are sooty brown on the upper surface and grey to brown, with tiny black white-rimmed spots, on the underside. It looks very much like a female blue.

Subspecies: The nominate subspecies occurs in southern British Columbia, and subspecies semiluna, which has the spots on the underside better developed, has been found in southwestern Alberta.

Range: The Sooty Hairstreak has a spotty distribution in the western U.S. It occurs in Canada at Osoyoos and Keremeos in British Columbia, and there is an old record from Waterton Lakes in Alberta.

Similar Species: Most likely to be confused with the dark females of Boisduval's Blue (Icaricia icarioides), which has whiter fringes and has a black discal spot in the centre of the forewing below, and often above as well. [compare images]

Early Stages: The larva of this species, in keeping with the appearance of the adult, feeds on the same foodplant, lupines (Lupinus spp.), as Boisduval's Blue. It is undescribed.

Abundance: The Sooty Hairstreak is uncommon to rare in most of its range.

Flight Season: Adults fly in late June and July in Canada.

Habits: The Sooty Hairstreak is always found near lupines, often in sagebrush areas at middle altitudes in the mountains. It should be looked for in fields, meadows, and along roadsides where lupines grow.

Remarks: Despite its blue-like appearance, foodplant use, and patrolling behaviour, this species is definitely a hairstreak. The reasons for this convergence are unknown, although the fact that the larvae of Boisduval's Blue, like those of many blues, are tended and protected by ants may be a clue.

© 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.

The Toronto Entomologists' Association thanks Agriculture and Agri-Food Canada for providing the content and computer code for this web page.