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:
Brown, J.W., Real, H.G., and D.K. Faulkner. 1992. Butterflies of Baja California. Lepidoptera Research Foundation, Beverly Hills, Calif. Comstock, J.A. 1927. Butterflies of California. Privately published, Los Angeles, Calif. [Facsimile available from Entomological Reprint Specialists, Los Angeles, Calif.] Dameron, W. 1997. Searching for butterflies in southern California. Flutterby Press, Los Angeles, Calif. Emmel, T.C. Editor. 1998. Systematics of western North American butterflies. Mariposa Press, Gainesville, Florida. Emmel, T. C. and J. F. Emmel. 1973. The Butterflies of Southern California. Natural History Museum of Los Angeles County Science Series No. 26. Garth, J.S. and J.W. Tilden. 1986. California Butterflies. California Natural History Guide 51. University of California Press, Berkeley and Los Angeles. Langston, R.L. 1981. The Rhopalocera of Santa Cruz Island, California. Journal of Research on the Lepidoptera 18: 24-35. Miller, Scott E. 1985. Butterflies of the Califorenia Channel Islands. Journal of the Research on the Lepidoptera 23: 282-296. Opler, Paul A. 1999. Peterson Field Guide to Western Butterflies, revised edition. Houghton Mifflin Co., Boston, Mass. Orsak, L.J. 1977. The Butterflies of Orange County, California. Museum of Systematic Biology, University of california, Irvine. Stanford, R.E. and P.A. Opler. 1993. Atlas of Western USA Butterflies. Privately published, Denver, Colo. Steiner, J. 1990. Bay Area Butterflies: The Distribution and Natural History of San Francisco Region Rhopalocera. Hayward, Calif.: Hayward State University, Masters Thesis. Tilden, J.W. and A.C. Smith. 1986. A Field Guide to Western Butterflies. Houghton Mifflin Co., Boston, Mass. Tilden, J.W. 1965. Butterflies of the San Francisco Bay Region. California Natural History Guide 12. University of California Press, Berkeley and Los Angeles.