Western Sulphur (Colias occidentalis Scudder)
Wing span: 1 3/4 - 2 1/2 inches (4.5 - 6.3 cm).
Identification: Upperside of male bright yellow with wide black border; orange morph is orange with yellow at costa and wing bases. Female pale yellow to greenish white with border blurry, incomplete, or absent; orange morph dull orange with wide black borders and dark veins. Underside of both sexes with pink wing fringes and golden yellow hindwing; orange morph green-gray to orange; both with dark overscales.
Life history: Males patrol in valleys or open areas near host plants for females. Females lay eggs singly on host plant leaves. Late-stage caterpillars hibernate.
Flight: May-August, mainly June-July.
Caterpillar hosts: Plants of the pea family (Fabaceae) including vetch (Vicia angustifolia), sweet vetch (Hedysarum), lupines (Lupinus), and white sweet clover (Melilotus alba).
Adult food: Flower nectar.
Habitat: Open areas including meadows, sagebrush flats, conifer forest openings, power-line cuts.
Range: Extreme southern British Columbia and northwestern United States south to north coastal California and central Utah.
Conservation: Some populations affected by grazing and fire suppression.
Management needs: Not reported.
The Nature Conservancy Global Rank: G3, G4 - Very rare or local throughout its range or found locally in a restricted range OR Apparently secure globally, though it might be quite rare in parts of its range, especially at the periphery. Subspecies chrysomelas is T2,T3 and is threatened by fire suppression, improper logging, and invasive alien weeds.
Ferris, C.D. and F.M. Brown. 1981. Butterflies of the Rocky Mountain States. University of Oklahoma Press, Norman. 442 pages. Garth, J.S. and J.W. Tilden. 1986.California Butterflies. University of California Press, Berkeley and Los Angeles. 246 pp, 24 plates. Layberry, R.A., P.W. Hall, and J.D. Lafontaine. 1998. The Butterflies of Canada. University of Toronto Press, Toronto. 282 pages, 32 color plates. Opler, P.A. 1999. A field guide to western butterflies. Houghton-Mifflin Co., Boston, Mass. 540 pages, 44 color plates. Opler, P. A. and V. Malikul. 1992. A field guide to eastern butterflies. Peterson field guide #4. Houghton-Mifflin Co., Boston. 396 pages, 48 color plates. Scott, J. A. 1986. The butterflies of North America. Stanford University Press, Stanford, Calif. 583 pages, 64 color plates. Stanford, R. E. and P. A. Opler. 1993. Atlas of western USA butterflies including adjacent parts of Canada and Mexico. Denver and Fort Collins, CO.
Author: Jane M. Struttmann
State and Regional References:
Elrod, M.J. 1906. The Butterflies of Montana. Bulletin of the University of Montana 30: 1-174. Ferris, C.D. and F.M. Brown. 1980. Butterflies of the Rocky Mountain States. University of Oklahoma Press. Norman. Layberry, R.A., Hall, P.W. & Lafontaine, D.J., 1998. The Butterflies of Canada. University of Toronto Press, Toronto, ON. 280 pp. Opler, Paul A. 1999. Peterson Field Guide to Western Butterflies, revised edition. Houghton Mifflin Co., Boston, Mass. Stanford, R.E. and P.A. Opler. 1993. Atlas of Western USA Butterflies. Privately published, Denver, Colo. Tilden, J.W. and A.C. Smith. 1986. A Field Guide to Western Butterflies. Houghton Mifflin Co., Boston, Mass.