Western White
Pontia occidentalis
Description 1 1/4-1 3/4" (32-44 mm). Male white above with network of black marginal and submarginal spots on FW tip and black FW cell spot. Male has olive-green scaling on veins and toward tips on HW below. More marking in female, with black network extending onto HW above. Spring brood more heavily marked than summer; all have greenish vein-scales below.
Similar Species Becker's White has brighter green veins, less but bolder black marking. Checkered White summer male lacks greenish veins; summer female lacks heavy black, but male and female spring butterflies are very similar.
Life Cycle Caterpillar dull green, light- and dark-banded; feeds on various crucifers (Brassicaceae) and spider plants or bee plants (Cleome, family Capparaceae).
Flight April-September, depending on altitude.
Habitat All sunny mountain habitats including arctic-alpine, but also lowlands in clearings, fields, and roadsides.
Range Alaska and British Columbia to Manitoba, south between Pacific Coast ranges and eastern fringes of Rockies to central California and New Mexico.
Discussion The Western and Checkered whites are very closely related, but they have definite ecological differences. The Western White is strictly adapted to mountains and northern habitats and the Checkered White to lowlands. The ranges of the 2 species overlap between the highlands and the plains, where these butterflies can be extremely confusing, even for practiced lepidopterists. Western Whites often fly high into the arctic-alpine zone, where they are one of the most common butterflies.
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