This butterfly is a state-designated threatened species.
The uppersides of the wings of both sexes are brown in color. The male has a long oval dark spot on the leading edge of the forewing. On the undersides of the wings of both sexes, the postmedian line of the forewing is irregular and that of the hindwing is faint. The hindwing has a submarginal black spot above the tail. Its wingspan is 1” to 2.5”.
The female lays eggs singly on its host plant, the wild blue lupine. In other parts of its range, the frosted elfin also utilizes wild blue indigo. Once hatched, the larvae feed on lupine flowers and the developing seedpods. Larvae are present for roughly three weeks, consuming the lupine flowers and seedpods as they move down the plant to pupate. The pupae overwinter in loose cocoons in the litter beneath the host plant. As adults, the frosted elfin rarely collects nectar. There is one brood per season. In this area, the flight occurs early May to early June. The males are highly territorial and will position themselves at the edges of their habitat or along pathways to the habitat.
The frosted elfin’s use of the wild blue lupine complements that of the Karner blue butterfly with the frosted elfin larvae feeding on the flowers and seedpods and the Karner blue larvae feeding on the leaves.