Satyrium fuliginosum
Sooty Hairstreak

Family Description:

Caterpillar: The caterpillar is light green, marked with white ">"-shaped spots on the side, and has a dark brown head. It reaches an average, full-grown length of to 1 inch.
Adult: The butterfly is small, with a wingspan of 1 to 1 inches. The upperside varies in color from dark gray to grayish brown to dark brown, and is unmarked. The underside is lighter in color, ranging from gray to grayish brown, and may be marked with one or two rows of black spots, each ringed with white. The black spots are smaller and their accompanying white rings larger on the hindwing compared to the forewing. The wings have a rounded appearance, and are fringed with grayish brown. While most Hairstreaks have a thin tail extending from the rear of the hindwing, this species does not.

This species has a patchy range which covers southern British Columbia and Alberta south to central California, and extends east to Montana, Wyoming, and Colorado. It occurs through most of the southern half of Idaho.

It occurs in dry, often hilly areas, including sagebrush steppe, mountainsides, forest openings, fields, and along roads. It is always found in conjunction with lupines (Lupinus spp.).


Caterpillar: Caterpillars feed at night on lupines (Lupinus spp.).
Adult: Butterflies drink flower nectar, often from wild buckwheat (Eriogonum spp.) and yellow flowers belonging to the sunflower family (Asteraceae).

Eggs are laid in the fall, overwinter, and hatch in the spring. There is only one generation of caterpillars each year. 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. Each caterpillar undergoes four stages of growth, called instars. Adults generally fly from mid-June to August. This species resembles females of the species Plebejus icariodes, the Common Blue, in both appearance and ecology.

Males patrol in search of receptive females and sometimes perch to wait for them. Greenish white eggs are laid singly on lupines or on nearby leaf litter.

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

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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).

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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.