Upperside of male lilac-blue with dark borders. Female may be brown, or blue with wide dark borders. Below, black or white postmedian spots are larger on forewing than on hindwing. Males patrol during the day near host plants for females. Eggs are laid on new growth of host plants.
Caterpillars feed first on leaves, then flowers and seedpods.
Caterpillars produce a sugary secretion which is eaten by the ants that protect them. Second-stage caterpillars hibernate. Nectar from flowers including Eriogonum and various composites. British Columbia east to the western edge of the Great Plains, south to New Mexico, Arizona, southern California, and Baja California. The Mission Blue, subspecies missionensis , is endangered in California.