Satyrium acadica
Acadian Hairstreak

Family Description:
Alternate Common Name:
Northern Willow Hairstreak.
Caterpillar: The caterpillar is bright green and marked along the side with a white stripe and yellowish white diagonal dashes and along the back with a wide, darker green band.
Adult: The butterfly is fairly small to medium-sized, with a wingspan of 1 1/8 to 1 1/2 inches. The upperside is grayish brown and may be marked with a single orange spot on the hindwing, usually in females. The underside is silvery gray and marked with a curved row of small black dots followed towards the outside by a curved row of orange ">"-shaped spots. The orange spots are larger towards the trailing edge of the hindwing. A thin tail extends from the hindwing; a large, bluish gray spot tipped with orange marks the hindwing near where the tail originates.

This species is found in Canada from southeastern British Columbia east to Nova Scotia, and in the U.S. from Idaho to the east coast, extending south as far as Colorado, east to northern Virginia. In Idaho, it occurs in the northern and south central parts of the state.

This species can be found in moist habitats such as along streams and in wet fields and meadows.


Caterpillar: Caterpillars feed on the leaves of willows (Salix spp.).
Adult: Butterflies drink flower nectar, commonly from milkweeds (Asclepias spp.) and dogbane (Apocynum spp.).

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. Adults generally fly from June through August. The tails of the hindwings of the butterfly resemble antennae and can act to fool predators into biting the wrong end of the butterfly, allowing it to escape. This species closely resembles the California Hairstreak and it can be difficult to distinguish between the two where their ranges overlap. However, the California Hairstreak occurs near oaks (Quercus spp.) while the Acadian Hairstreak occurs near willows (Salix spp.).

Males perch in the afternoon on short vegetation near willows to wait for receptive females, and may occasionally actively patrol for them. Females lay white eggs, tinted with green or pink, on the twigs of willows.

Idaho Status: Unprotected nongame species.
Global Rank: G5; populations are widespread, abundant, and secure.

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.