Margined White (Pieris marginalis) (Scudder, 1861)
Diagnosis: This species is similar to the Mustard White (P. oleracea) and replaces it in the west. The dark scaling on the veins on the underside is a duller, more diffuse, grey green, not sharply contrasting dark green as in the Mustard White. In females the amount of dark shading on the veins above varies from a slight amount to extensive, with a dark patch near the middle of the forewing and another dark patch on the lower margin. Females from higher-elevation or wetter habitats are darker than those from lower or drier habitats. Second-generation adults (mostly in southern British Columbia) are mainly white; females have the two dark patches on the forewing. Wingspan: 35 to 47 mm.
Subspecies: The nominate subspecies occurs in Canada.
Range: The Margined White occurs from southeastern Alaska southward through British Columbia and the Rocky Mountains of southwestern Alberta (with a disjunct population in the Cypress Hills, on the Alberta/Saskatchewan border) to New Mexico, Arizona, and California.
Early Stages: The larva is similar to that of the Mustard White and also feeds on Brassicaceae.
Abundance: Pieris marginalis is fairly common in most of its range in Canada.
Flight Season: In Alberta and most of British Columbia there is one generation per year between mid-May and early August. In southern British Columbia adults appear in early April, with a second generation in July and August.
Habits: This butterfly occurs in a range of habitats from dry, open pine forests to wet coniferous forests on the west coast.
Remarks: Pieris marginalis occurs with Mustard White (P. oleracea) in the Rocky Mountain foothills of Alberta and in northeastern British Columbia and with Arctic White (P. angelika) in northwestern British Columbia.
© 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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