Northwestern Fritillary (Speyeria hesperis) (W.H. Edwards, 1864)
Diagnosis: A relatively small (wingspan: 45 to 58 mm) fritillary, with a bright orange upperside (yellow in females) and thinner black markings than most fritillaries. The most distinctive form is the prairie subspecies lais, in which the black spot near the base of the forewings, which is prominent in Atlantis Fritillary and Aphrodite Fritillary, is reduced or absent; the wing margins are usually orange, not black-filled as in atlantis; the underside of the hindwing is a washed-out reddish brown with the colour appearing uneven, tending to be concentrated in patches around the silver spots; the pale-yellowish submarginal band is wide. Subspecies beani and the form found in most of British Columbia are not as distinctive, but differ from atlantis in their smaller size, wider pale submarginal band on the hindwing below, and colour of the underside of the hindwing. In western Canada this is purplish brown, like eastern atlantis, but in western Canada atlantis subspecies hollandi has the underside a dark olive brown.
Subspecies: Three subspecies occur in Canada. Subspecies lais occurs in open prairie habitat from Manitoba to Alberta. Subspecies beani is primarily an aspen parkland subspecies that occurs from Manitoba to Alberta and into southern Northwest Territories and the Peace River District of British Columbia. Specimens from most of British Columbia probably represent an unnamed subspecies; they are larger than subspecies beani, being similar in size and colour to Speyeria atlantis canadensis from eastern Canada; their identity as a subspecies of Speyeria hesperis comes mainly from intergradation with subspecies beani and co-occurrence without intergradation with atlantis subspecies hollandi in British Columbia.
Range: The Northwestern Fritillary occurs from southwestern Manitoba west through most of Saskatchewan, Alberta, and British Columbia (except on the coast). There are six records from Yukon, north to Dawson, and a few from the Northwest Territories, along the Slave and Mackenzie Rivers, north to Fort Norman.
Similar Species: The Northwestern Fritillary is most likely to be confused with the Aphrodite Fritillary and Atlantis Fritillary. Speyeria atlantis prefers moist conifer woodlands and bog margins, while hesperis occurs in drier habitats such as open prairie and dry aspen and spruce forests. In the Prairies, Speyeria hesperis lais closely resembles Speyeria aphrodite, but can be identified by its smaller size, the small black spot at the base of the forewing, the wider pale submarginal band on the hindwing below, and the presence of sex scales in males, discussed under Speyeria aphrodite. Distinguishing characteristics between atlantis and hesperis are discussed above in the Diagnosis and Subspecies sections. [compare images]
Early Stages: These are unknown.
Flight Season: This species generally flies from midJune to mid-August, but is most common in July.
Habits: The Northwestern Fritillary is found mostly in dry open meadows and hillsides in the Prairies and dry open forests of aspen, spruce, fir, and Douglas-fir in the aspen parkland and British Columbia. Like other Speyeria it frequently visits flowers.
Remarks: The discovery that lais and hollandi fly together in some parts of Manitoba, apparently without interbreeding, led Howe (1975) to treat all of the western fritillaries of this group as Speyeria electa (= S. hesperis), with subspecies dennisi (=lais) being a prairie subspecies, and Atlantis Fritillary being an entirely eastern species, with hollandi as its westernmost subspecies in Manitoba. Howe based this on the lais/hollandi situation in Manitoba, while stating that Speyeria electa from Colorado can frequently be distinguished from Speyeria atlantis from the Appalachians only by the locality labels. The two groups of populations were later combined under Speyeria atlantis by Miller and Brown (1981) and Ferris (1989) because Speyeria atlantis and Speyeria hesperis are reported to hybridize in some parts of Colorado. More recently, Bird et al. (1995) have treated electa (subspecieslais and beani) and atlantis (subspecies hollandi) as separate species because they occur together in many parts of Alberta without evidence of hybridization. The same situation appears to be true through much of western Canada so we retain them as separate species. It is possible that similar-appearing forms in the two species have led to claims that they are hybridizing in the western U.S., when this has not actually been demonstrated.
© 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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