Threatened and Endangered Species - Status Reports
Date Published: July 1993
Number of Pages: 42
The Oregon silverspot butterfly (Speyeria zerene hippolyta) is federally and state listed as a threatened species. The silverspot occurred historically from Grays Harbor County in Washington to central Oregon and a disjunct population occurred in northern California. In Washington it was found along the coast from Westport to the Columbia River. Today all but eight localities (one in California, six in Oregon, and one in Washington) have been extirpated. The Washington population is restricted to one small area on the Long Beach peninsula, where intensive searches have revealed few adult butterflies. The most recent surveys in 1991 found no butterflies. It is likely that there is no longer a viable population in Washington.
The Oregon silvers pot butterfly occurs in three types of early successional grasslands with adjacent forest fringes: coastal salt spray meadows, stabilized dunes, and montane meadows. Within these grasslands, the silverspot has three primary requirements: 1) larval hostplants, 2) adult nectar sources and 3) wind protection. The larval stage of the butterfly is wholly dependent on the western blue violet (Viola adunca). The female lays her eggs on or near violet plants. When the larvae hatch, they find a place to overwinter until they emerge in the spring and begin feeding on the violets. The larvae pass through six ins tars before pupating and emerging as butterflies. Adults feed in meadows on nectar-producing herbaceous plants such as aster (Aster spp.), tansy ragwort (Hypochaeris radicata), goldenrod (Solidago spp.), pearly everlasting (Anaphalis margaritacea), false dandelion (Hypochaeris radicata), and thistle (Cirsium spp.), and seek refuge in adjacent forest fringes for protection from strong coastal winds.
Habitat destruction is the cause of the decline of the Oregon silverspot in Washington, as elsewhere. Seaside meadow sites have been developed for residential and business establishments, public parkland development, and parking areas or lawns. Excessive use of salt-spray meadows by grazing animals and off-road vehicles has destroyed habitat. Fire suppression, herbicide/pesticide applications, and the introduction of non-native plants have also contributed to the decline of this buttertly. The Department of Wildlife has been conducting management and recovery efforts aimed at acquiring and restoring suitable habitat since 1990. It is expected that in order to recover this species it will be necessary to reintroduce butterflies to restored habitat. These techniques have been developed in Oregon and have proven successful.
The Oregon silverspot butterfly population in Washington has declined to the point where it may no longer be viable.
It is recommended that the Oregon silverspot butterfly be reclassified from threatened to endangered status.