Speyeria zerene behrensii (W.H. Edwards, 1869)
Date of listing: December, 1997
Federal Status: Endangered
State Status: None
Behren’s Silverspot Butterfly is in the Nymphalidae, or brush-footed butterfly family. It is one of three threatened or endangered subspecies of Speyeria zerene (along with Myrtle’s Silverspot and the Oregon Silverspot). It is similar in appearance to these, with golden brown and orange wings, dappled with brown spots and bands. The undersides of the wings bear silver spots, as indicated by the common name. Behren’s Silverspot is known only from coastal northern California.
Behren’s Silverspot adults mate and lay eggs in the mid- to late summer. The eggs hatch shortly thereafter and the 1st instar larvae enter a period of dormancy. The larvae resume feeding the following spring as their sole food plant, a Violet (Viola adunca) begins its spring growth. Following 2-3 months of feeding and 4 molts, the larvae pupate. After a short pupation, the adults emerge, living approximately 3 weeks during which they live to mate and drink nectar.
Behren’s Silverspot historically ranged from the Russian River in Sonoma County north to Pt. Arena in southern Mendocino County. Its preferred habitat is coastal terrace prairie. The butterfly is now only known from a single population at Pt. Arena. Coastal prairie throughout this area has been degraded by several factors, including development and the spread of exotic vegetation. Fire suppression has also likely played a role; the butterfly’s host violet is better able to germinate when the overlying debris has been cleared away by periodic fires.