Colias interior
Pink-Edged Sulphur

Family Description:
Caterpillar: The caterpillar is yellow-green, lightly dotted with black and marked with light or dark stripes along the back and a white and red stripe along the side.
Adult: This butterfly is medium-sized, with a wingspan of 1 to 2 inches. The male butterfly is bright yellow on the upperside and marked with black on the outside edges of the wings. The female is yellow to white on the upperside, with a lighter, incomplete black border on the wing edges. Both sexes have a faint spot on the forewing and an orangish spot on the hindwing. Underneath, the forewing is yellow to white and may have a small spot; the hindwing is yellow to white to gray, with a small white spot outlined in pink.  There is a noticeably pink fringe outlining the wings.

This species ranges from British Columbia, Alberta, and the Pacific Northwest, east across the southern portion of Canada to the coast, through the Great Lakes states and New England. There may be isolated populations in certain eastern states, including Pennsylvania, Maryland, and the Virginias. In Idaho, it can be found in the northern half of the state.

It is found in open areas, including forest openings, clearings, or burned areas, and bogs.


Caterpillar: Caterpillars feed on the leaves of blueberry (Vaccinium spp.).
Adult: Butterflies drink flower nectar, often from sarsaparilla (Aralia nudicaulis), orange hawkweed (Hieracium aurantiacum), and various asters (Aster spp.).

There is one generation of caterpillars each summer. The young caterpillars overwinter in a physiological state called diapause, and emerge in spring to feed, molt, and eventually pupate. Adults generally fly from mid-June to late August. The butterflies exhibit a slow flight.

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

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.