Shasta Blue (Plebeius shasta [W. H. Edwards])
Wing span: 7/8 - 1 1/8 inches (2.2 - 3 cm).
Identification: Upperside of male lilac blue with a wide dark border; female darker, may have orange band at outer margin of hindwing. Both sexes with dark cell bars on fore- and hindwings. Underside of both sexes gray with black postmedian spots; other spots are dark gray. Hindwing outer margin with iridescent green spots capped by a light band.
Life history: Males fly just above the ground to search for females. Eggs are laid singly on leaves of host plants; caterpillars feed on leaves and flowers. Where found above timberline, these butterflies require 2 years to mature, spending their first winter as eggs and the second winter as mature caterpillars.
Flight: One brood from June-August.
Caterpillar hosts: Various Astragalus, Lupinus, and Trifolium species of the pea family (Fabaceae).
Adult food: Flower nectar.
Habitat: Cushion-plant communities in forest openings, sagebrush hills, high plains, prairies, and alpine fell-fields.
Range: High elevations from Washington east to North Dakota and Nebraska; south to central California and Colorado.
Conservation: Not usually of conservation concern.
The Nature Conservancy Global Rank: G5 - Demonstrably secure globally, though it may be quite rare in parts of its range, especially at the periphery.
Management needs: Not reported.
Scott, J. A. 1986. The butterflies of North America. Stanford University Press, Stanford, Calif. 583 pages, 64 color plates. Tilden, J. W. 1986. A field guide to western butterflies. Houghton-Mifflin Co., Boston, Mass. 370 pages, 23 color plates.
Author: Jane M. Struttmann
State and Regional References:
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.