Plebejus [Icaricia] icarioides
Boisduval’s Blue

Family Description:
Alternate Common Names:
Common Blue, Lupine Blue.

This is a very small caterpillar, with an average, full-grown length of about 1/2 inch. It is typically green, striped lengthwise along the back with a reddish or darker green line, and marked on the sides with diagonal white dashes. It is covered with short white hair. Alternatively, it can be reddish purple in color.
Adult: This butterfly is large for a Blue, with a wingspan of 1 to 1 3/8 inches. Males are purplish blue on the upperside, while females are brown and possibly clouded with blue where the wings attach to the body. Both sexes are outlined in black and fringed with white. Underneath is white to gray to cream and marked with two curved, fairly even rows of black spots; the forewing spots are noticeably larger than those on the hindwing.

This species ranges from southern British Columbia and Alberta south to southern California and central Arizona and New Mexico, extending to the east as far as the western portions of the Dakotas and central Colorado. It occurs through most of Idaho.


It occurs in a variety of habitats, including sagebrush steppe, meadows, prairies, forest openings, and coastal dunes, but always near to where lupines are growing.


Caterpillar: Caterpillars feed on the leaves, flowers and fruits of many lupine species (Lupinus spp.), but seem to prefer new shoots in the spring.
Adult: Butterflies drink flower nectar, and males can often be found "puddling" at muddy seeps where they gather salts and other nutrients by sipping moisture.

The caterpillars sometimes rest during the day in holes dug by ants near host plants. The 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 only one new generation of caterpillars each summer. Young caterpillars overwinter in a physiological state called diapause, and emerge in spring to continue feeding, to molt, and eventually to pupate. Each caterpillar undergoes four stages of growth, called instars. Adults generally fly from April to mid-August. The adults are the largest Blues in North America.


Males actively patrol in search of receptive females. Females lay eggs singly on host plant leaves, often the underside; other plant parts may be chosen for oviposition as well. Typically, only one species of lupine is used in a given area, and it is often the one with the most pubescence (hair).

Idaho Status: Unprotected nongame species.
Global Rank: G5; most populations are widespread, abundant, and secure. One subspecies in California, P. icarioides missionensis, the Mission Blue, is listed as T1. This means it is critically imperiled because of extreme rarity and is imminently vulnerable to extinction.

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.