Plebejus [Icaricia] shasta
Shasta Blue

Family Description:
Alternate Common Names:
Cushion-Plant Blue, Alpine Blue.

The caterpillar varies in color from brown to green to white. It is marked with a black or brownish line or band along the back and on each side, and black diagonal dashes. It reaches an average length of 1/2 inch.
Adult: The butterfly is fairly small, with a wingspan of to 1 inch. The upperside of the male is purplish blue with a thick, dark brown border along the outer edge of the forewing. A similar border may edge the hindwing, or it may appear as a row of closely spaced large spots. Both the fore- and hindwing are usually marked with a single, crescent-shaped black spot. The upperside of the female is brown to bluish brown and marked similarly to the male. The hindwing is edged with a row of black spots edged with orange towards the inside. Underneath, both sexes are whitish gray to dark gray and often appear mottled. The underside of the forewing is marked with a curved row of blackish spots followed by two curved rows of brownish spots. The underside of the hindwing is marked with black and brownish spots and a curved row of greenish metallic spots along the outer edge, capped with orange or brown.

This species ranges from southern Alberta and Saskatchewan south through Montana to Colorado and Utah, and from central Oregon south to central California and Nevada. It occurs in Idaho in the southcentral and southeastern portions of the state.


It typically occurs at higher elevations on rocky slopes, in meadows, forest openings, sagebrush steppe, and prairie hills.


Caterpillar: Caterpillars feed on the leaves and flowers of various members of the pea family (Fabaceae), including lupine (Lupinus spp.), clover (Trifolium spp.), and milkvetch (Astragalus spp.).
Adult: Butterflies drink flower nectar.

Each caterpillar is equipped with a honey gland, also known as a dorsal nectary organ, which emits a sugary solution agreeable to ants. The ants feed on the solution and in turn protect the caterpillar from predators. Also for protection, the caterpillar bears a pair of everscible tubercles or tentacles on the eighth segment. These tubercles are usually housed within the body, but when the caterpillar feels threatened by the approach of a potential predator, they can be pushed out to release a chemical which mimics an ant alarm pheromone. This scent causes the ants to become frenzied and aggressive, and the potential predator takes leave or is eaten by the ants. There is one generation of caterpillars each year throughout its range. Each caterpillar undergoes four stages of growth, or instars. In much of its range, it is a biennial species requiring two years to complete its life cycle. Eggs laid in the summer overwinter and hatch in the spring. The caterpillars then feed and molt during the following summer and overwinter in a physiological state called diapause, emerging in spring to pupate. Adults generally fly from June through July, sometimes flying into September. The butteflies generally fly only a few inches above the ground.


Males actively patrol in search of receptive females. Females lay their eggs singly primarily on the leaves of host plants.

Idaho Status: Unprotected nongame species.
Global Rank: G5; populations are widespread, abundant, and secure.

Ballmer, G. R. and G. F. Pratt. 1988. A survey of the last instar larvae of the Lycaenidae of California. Journal of Research on the Lepidoptera 27:1-81.

Ferris, C. D. and F. M. Brown. (eds.) 1981. Butterflies of the Rocky Mountain States. Univ. of Oklahoma Press, Norman, Oklahoma, USA, 442 pp.

Opler, P. A., H. Pavulaan, and R. E. Stanford. 1995. Butterflies of North America. Jamestown, North Dakota, USA: Northern Prairie Wildlife Research Center Home Page. (Version 05Nov98).

Opler, P. A. and A. B.Wright. 1999. A Field Guide to the Western Butterflies.   Second Edition.  Peterson Field Guide Series. Houghton Mifflin Company, New York, New York, USA, 540 pp.

Pyle, R. M. 1981. National Audubon Society Field Guide to North American Butterflies. Alfred A. Knopf, Inc., New York, New York, USA, 924 pp.

Scott, J. A. 1986. The Butterflies of North America. Stanford University Press, Stanford, California, USA, 583 pp.

Stanford, R. E. and P. A. Opler. 1993. Atlas of Western U.S.A. Butterflies (Including Adjacent Parts of Canada and Mexico). Published by authors, Denver, Colorado, USA, 275 pp.