The Mission Blue lays eggs only on lupines. The larvae feed on its leaves and stems, and blend in well with the hairy leaves. Four lupine species have been observed as host plants for eggs and larvae. These are the silver lupine Lupinus albifrons, summer lupine Lupinus formosus, the varied lupine Lupinus variicolor, and Lupinus nanus. The species differ in a myriad of ways - habitat, ecology, growth form, and morphology.
Lupines are only found in the grasslands and rocky outcrops. Lupines cannot survive in the shade of shrubs such as coyote brush, among forests of oaks and Douglas firs, or in the wet ravines of willows. Lupine - grasslands are very rare habitats on the San Francisco Peninsula. This is part of the reason why the population of the Mission Blue is small, and it is in danger of becoming extinct.