Colias scudderii

Colias scudderii, the willow sulphur, is a butterfly in the Pieridae family. It is found from Alaska south through the Rocky Mountains to northern New Mexico. The habitat consists of mountain meadows and willow bogs.

The wingspan is 38–51 mm (1.5–2.0 in). The upper surface of the males is lemon yellow with a dark wide border cut by yellow veins. Females are often white, with a small black cell spot. The border is incomplete or lacking. The underside of both sexes is dirty green. Adults are on wing from June to August. They feed on flower nectar.

The larvae feed on the leaves of Salix species (including Salix reticulata, Salix lutea and Salix planifolia). Second, third, and fourth instar larvae hibernate.