Lycaeides idas
Northern Blue

Family Description:
Some authors refer to this species as Lycaeides argyrognomon, and others list it with the genus name Plebejus. This species is very similar to the Melissa Blue (L. melissa) and in certain parts of its range can only be distinguished by dissection.

The appearance of the caterpillar varies from greenish to brownish, and it may be marked with reddish lines along the back and faint whitish marks on the side. Its average, full-grown length is 1/2 inch.
Adult: This is a small to medium-sized butterfly, with a wingspan of 7/8 to 1 1/2 inches, and its appearance is variable. Generally, the male is shiny purplish blue on the upperside, with a thin black outline and white fringe. The female is bluish gray to brown, fringed with white, and marked with a row of brownish orange spots along the rear of the hindwing, possibly extending more faintly along the edge of the forewing. Underneath, both sexes are grayish white to light brown and dotted with black. The edges of the wings, especially the hindwing, may be marked with a curved row of orange spots; additionally, there may be silvery green spots here as well. There is a black line outlining the wings that becomes a line of connected dots on the hindwing.

This species is holarctic, which means it occurs in the temperate regions of the Northern Hemisphere. In North America, it ranges from Alaska south and east across Canada to the east coast; south through western Washington and Oregon to central California; in portions of Idaho, Montana, Wyoming, and Colorado; and in the Great Lakes states.


It occurs in open areas including tundra, meadows, forest openings, and bogs.


Caterpillar: Caterpillars feed on various members of the heath family (Ericaceae) in the eastern part of its range, and on legumes (Lupinus, Astragalus, and Lotus spp.) in the west.
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 one generation of caterpillars each summer. Each caterpillar undergoes four stages of growth, called instars. Both eggs and young caterpillars can overwinter in a physiological state called diapause. Adults generally fly from June to early October.


Males actively patrol, most often near host plants, in search of receptive females. Females lay eggs singly on the stems of host plants or in the litter below.

Idaho Status: Unprotected nongame species.
Global Rank: G5; most populations are widespread, abundant, and secure. However, subspecies L. idas lotis of California is ranked as T1, which 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.