Rosner's Hairstreak
Callophrys rosneri (Johnson, 1976)

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Diagnosis: The upper surface of the tailed wings of the male are dark brown with some cinnamon-brown patches, particularly on the outer third of the wings; the female has cinnamon-brown wings, with a contrasting dark brown border on the wing margins. The underside is brown with a violet tint, especially on the hindwings. The white-edged band running the length of the wings is usually irregular. There is a row of three or four dark spots on the hindwings above the marginal hoary grey patch. Wingspan: 21 to 27 mm.

Subspecies: Two subspecies are reported to occur in Canada by Johnson (1976); nominate rosneri, which occurs in the interior ranges, is slightly more reddish brown on the hindwing beneath than subspecies plicataria, which occurs on Vancouver Island and in the Coastal Range.

Range: Callophrys rosneri is found throughout southern British Columbia wherever the larval foodplant Western Red Cedar occurs.

Similar Species: Barry's Hairstreak (C. barryi). Where the two species occur together, they are best identified by habitat, since Rosner's Hairstreak is closely associated with Western Red Cedar (Thuja plicata) whereas Barry's Hairstreak is closely tied to Rocky Mountain Juniper (Juniperus scopulorum). See also Johnson's Hairstreak (C. johnsoni). [compare images]

Early Stages: The larva has a series of yellow crescent-shaped oblique dashes on each side. It is apparently restricted to Western Red Cedar.

Abundance: Local and spotty in distribution, it can be common where its foodplant occurs.

Flight Season: Adults are on the wing from mid-April until early June.

Habits: Rosner's Hairstreak stays close to forests where its larval foodplant Western Red Cedar occurs. Males usually perch on the foodplants waiting for females.

Remarks: Rosner's Hairstreak and the next species belong to a confusing and poorly understood group of hairstreaks. Johnson (1976) arranged populations formerly associated with Nelson's Hairstreak (Callophrys nelsoni (Boisduval)) into five species based to a large degree on foodplant differences and slight differences in the genitalia. Scott (1986) took quite a different view and not only lumped these five species together but treated Johnson's five species as populations or subspecies of the Juniper Hairstreak (Callophrys grynea). Two species in this group occur in British Columbia and in spite of the small differences between them, the biological and behavioural evidence supports their treatment as valid species. Rosner's Hairstreak occurs through southern British Columbia and is restricted to Western Red Cedar; the larvae feed on it and the adults perch on it for mating. It occurs in many areas of southern British Columbia with Barry's Hairstreak, but this species can usually be identified by the greyer colour of the hindwing below, and by its close association with Rocky Mountain Juniper. There are supposed to be subtle differences in the genitalia between these two species, and between them and the Juniper Hairstreak, but our dissections have failed to confirm these claims. Rosner's and Barry's Hairstreaks have been studied in detail by Crispin Guppy in the Victoria area and he has confirmed that they appear to be valid species, at least in that area. Both species will feed on the "wrong" foodplants in captivity, but apparently do not do so in nature. The situation appears to be more complicated farther south, since Rosner's and Barry's Hairstreaks are said to hybridize at some locations in Oregon (Paul Hammond, pers. comm). Another possibility in need of further study is that Rosner's Hairstreak may be a distinct species but Barry's Hairstreak may be a western subspecies of the Juniper Hairstreak.

© 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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