Pontia occidentalis
Western White

Family Description:
Caterpillar: The caterpillar is green and ringed with alternating light and dark bands.
The butterfly has a wingspan of 1 to 2 inches. Its coloration and markings vary both between the sexes and with the time of year. Generally, the upperside is white and marked with black and gray. Specifically, the forewing is bordered by a row of triangle-shaped, blackish spots, followed by an incomplete row of similar spots. There are two black spots, one on the leading edge and one near the inside edge. The hindwing has a black or faint gray border marked with white, diamond-shaped spots. The veins may be marked in gray, especially in females. Underneath, the wings are white and marked with grayish green lines, at the tip of the forewing and over the entire hindwing. Periods of short daylength (in the spring and fall) result in butterflies with the most pronounced markings.

This species ranges from Alaska south and east across Canada to western Ontario. In the U.S., it occurs throughout the northwest quarter, as far south as central California to central Colorado. It can be found throughout most of Idaho.

It occurs in sunny, open areas, such as alpine meadows, open plains, fields, and in the arctic.


Caterpillar: Caterpillars feed on various parts of members of the mustard family (Brassicaceae) and the caper family (Capparaceae).
Adult: Butterflies drink flower nectar.

There is one generation of caterpillars each summer in the northernmost part of its range, and two to three where the climate is more mild. Pupae of the last generation overwinter in a physiological state called diapause. Adults generally fly from February to November in most of its range, but may fly only in June and July where the climate is harsh.

Males actively patrol in search of receptive females. Females lay eggs singly on 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. http://www.npwrc.usgs.gov/resource/distr/lepid/bflyusa/bflyusa.htm (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.