Myrtle’s Silverspot Butterfly

Larvae can remain in diapause for a year or more. Adults live for up to five weeks.

The Myrtle’s silverspot butterfly reproduces once per year as a species. Adult Myrtle’s silverspot butterflies emerge from their pupae between mid-June and mid-July and live two to five weeks. The total flight period, however, lasts for two to three months, from mid-June to early October, since adult emergence is staggered. Females lay one egg at a time solely on the dried leaves and stems of the host plant, Viola adunca. The number of eggs females lay is highly correlated with the amount of nectar they consume.

Larvae emerge from their eggs a few weeks after being laid. New larvae migrate a short distance into suitable foliage or leaf litter and spin a silk web where they remain in a suspended and inactive state known as diapause through the fall and winter. In spring, diapause ends and larvae begin searching for and feeding on the fresh leaves of the host plant. Larvae feed for 7 to 10 weeks and then form a cocoon from leaf debris and silk. The pupal stage for the Myrtle’s silverspot butterfly lasts for about two weeks.

Emergence from the cocoon typically occurs from mid-June to mid-July. Adults are active during calm weather between mid-June and early October and inactive during windy and foggy periods. They can travel miles if needed in search of nectar, mates, or violets. Adults live up to five weeks.

The larval host plant for the Myrtle’s silverspot butterfly is Viola adunca, known as western dog violet. This violet serves as the only known larval food plant for Myrtle’s silverspot butterfly, while a variety of other native plants, like gumplant, western pennyroyal, yellow sand verbena, seaside daisy and mule ears, as well as non-native plants, like bull thistle and Italian thistle, serve as nectar sources for the adult butterflies.

Myrtle’s silverspot butterfly is found among coastal dunes, coastal prairies and coastal scrub that are protected from winds and have the caterpillar’s host plant, Viola adunca. The mature butterfly also requires a variety of nectar sources. The coastal areas inhabited by the Myrtle’s silverspot butterfly are commonly buffeted by strong onshore winds, and, although the adults are known to be fairly strong flyers, the butterfly is more often active on days with low wind. The caterpillar’s host plant, Viola adunca, is typically found in damp banks or on the edge of forest meadows.

Myrtle’s silverspot is a medium-sized butterfly with a wingspan averaging 2.1 to 2.3 inches.

The upper sides of the fore and hind wing surfaces are golden brown to reddish brown with many conspicuous black spots, lines and other markings, sometimes with a greenish tinge basally. The undersides are light tan, reddish brown, and brown with black lines and distinctive silver spots and black spots. The base of the wings and the body are densely covered with hairs.

The larval host plant for the Myrtle’s silverspot butterfly is Viola adunca, known as western dog violet. This violet serves as the only known larval food plant for Myrtle’s silverspot butterfly, while a variety of other native plants, like gumplant, western pennyroyal, yellow sand verbena, seaside daisy and mule ears, as well as non-native plants, like bull thistle and Italian thistle, serve as nectar sources for the adult butterflies.