Colias eurytheme
Orange Sulphur

Family Description:
Alternate Common Name: Alfalfa Butterfly.
Caterpillar: The caterpillar is dark green, marked lengthwise with pinkish and white side stripes, and covered with white hair.
Adult: The butterfly is medium-sized to large, with a wingspan of 1 3/8 to 2 3/4 inches. It varies in color regionally, seasonally, and between the sexes. Generally, males are yellow to orange on the upperside, marked with a thick black border, a small black spot on the forewing, and possibly a small orange spot on the hindwing. Females can be orange to yellow to white and marked similarly, but the border is irregular and interrupted with yellow spots. The underside of both sexes can be orange to yellow to greenish yellow, with the edges of the wings fringed in pinkish white. The underside of the fore- and hindwings may each have a white spot outlined in brown or black,  with the forewing spot appearing darker and the hindwing spot topped with a tiny, second spot. A faint row of dark spots spaced apart spans the outer portion of the underside of both wings.

This is a widespread species, found throughout southern Canada and the continental U.S., south to central Mexico. It occurs throughout Idaho.

It is most often found in open areas, such as lawns, meadows, and fields, particularly those with clover or alfalfa.


Caterpillar: Caterpillars eat the leaves of legume plants, such as alfalfa (Medicago sativa), milk vetches (Astragulus spp.), and clovers (Trifolium and Melilotus spp.).
Adult: Butterflies drink flower nectar.

Caterpillars typically feed at night. When young, they chew holes in the tops of leaves; later they feed on the tips of leaves, while the oldest caterpillars eat one side of a leaf at a time. There can be two to three generations of caterpillars each summer in the north, and up to five in the south. Either the older caterpillars or the pupae of the last brood of the season overwinter in a physiological state called diapause. Adults generally fly from May through October. Large numbers of adult males can frequently be observed congregating at muddy sites where they obtain salt and nutrients, a behavior called puddling. This species can occasionally hybridize with the Common Sulphur, Colias philodice, where both are present. The Orange Sulphur is one of the most common butterflies in North America, and the caterpillars’ presence in large numbers can cause significant damage to alfalfa crops.

Males actively patrol in search of receptive females. Females lay eggs singly on host plant leaves, often on the upperside.

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.