Plebejus [Icaricia] lupinus
Lupine Blue

Family Description:
Alternate Common Name:
Large Silver-Studded Blue.
Note: The distinctions between this species and the Acmon Blue, Plebejus [Icaricia] acmon, are unclear and debated by scientists. Some authors refer to this species as Plebejus [Icaricia] lupini.

Caterpillar: The caterpillar is greenish, sometimes reddish, and marked with a dark stripe along the back and variable markings on the side. It is covered with fine white hair. The average, full-grown length of the caterpillar is 1/2 to 3/4 inch.
Adult: This is a small butterfly, with a wingspan of 3/4 to 1 1/8 inches. The male is purplish blue on the upperside while the female is dark brown. Both sexes are outlined in black, fringed with white, and marked with a curved orange band near the edge of the hindwing. In some males this band may be divided into a series of separate spots. Underneath is grayish white and marked with black spots arranged in curved rows. The underside of the hindwing is marked by a curved orange band which may be tipped with metallic green towards the outside.

This species occurs in parts of central Washington and Oregon, south into California and Nevada. It also occurs in patches of northern and west central Idaho.

It can be found at moderate elevations in open areas such as meadows, chaparral, rocky outcrops, and forest openings.


Caterpillar: Caterpillars feed on the flowers of wild buckwheat (Eriogonum spp.).
Adult: Butterflies drink flower nectar.

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 in the Sierra Nevadas of California but there are several elsewhere in its range. Young caterpillars overwinter in a physiological state called diapause. Adults generally fly from March through September. This species’ name is not accurately descriptive, as its caterpillar does not feed on lupines, while many other species of Blues do.

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

Idaho Status: Unprotected nongame species.
Global Rank: G4; population levels are secure, but may be of concern in the future.

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.

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.