Hemiargus isola
Reakirt’s Blue

Family Description:
Alternate Common Names:
Solitary Blue, Mexican Blue.
Note: This species is referred to by the genus name Echinargus by some authors; others consider Echinargus to be a subgenus of Hemiargus.

Caterpillar: The caterpillar is light green and marked with red. Its average, full-grown length is reported to be 1/2 inch.
Adult: The butterfly is small to medium-sized, with a wingspan of 3/4 to 1 1/8 inches. The male is light purplish blue on the upperside, while the female is bluish brown with blue where the wings attach to the body. The hindwing of both sexes may have one or two black spots near the outside edge. Underneath is brownish white and marked with a curved row of five or six black spots, outlined in white, on the forewing. The underside of the hindwing is marked with several smaller black or brown spots.

This species is a resident of the extreme southwestern U.S., Mexico, and Central America. It migrates north in the summer up to Nevada, southern Idaho, Wyoming, and east through the Plains states as far as Ohio.

It can be found in open areas such as fields, grasslands, meadows, and deserts.


Caterpillar: Caterpillars feed on the flowers, fruits, and young leaves of a variety of legumes, including acacias (Albizzia and Acacia spp.), indigos (Dalea and Indigofera spp.), and mesquite (Prosopis 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 are three or more generations of caterpillars each year. Each caterpillar undergoes four stages of growth, called instars. Adults migrate north in the summer, generally flying from March to Novemeber but occurring all year long in some parts of its range. While this species may overwinter in a physiological state of diapause in parts of its range, the stage in which it does so has not been observed or reported.

Males actively patrol in search of receptive females. Females lay eggs singly on the flower buds 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. http://www.npwrc.usgs.gov/resource/distr/lepid/bflyusa/bflyusa.htm (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.