Speyeria zerene myrtleae (Invertebrates)

Species Description

Myrtle’s Silverspot Butterfly (Speyeria zerene myrtleae) is a member of the brush-footed butterfly family (Nymphalidae). It is a medium-sized butterfly with a wingspan just over two inches. The upper sides of the wings are a beautiful golden brown with numerous black spots and lines. The undersides are tan, orange-brown and reddish brown with black lines and distinctive silver and black spots. Larvae are dark-colored with many sharp branching spines on their backs. The base of the wings and the body are densely covered with hairs. It flies during the summer, and it can travel many kilometers in search of food or a mate.

The species inhabits coastal dunes, coastal scrub, and coastal grasslands that provide adequate nectar sources and support the species’ larval host plant, western dog violet (Viola adunca). The Myrtle’s Silverspot naturally ranged from coastal San Mateo County near Pescadero northward to the Black Point area in northern Sonoma County. This put the species’ range squarely within lands that now comprise the GGNP, and historic records indicate the species was once found within some of the properties most recently acquired by the Park.

However, since 1992 the Myrtle’s Silverspot Butterfly has been listed as endangered under the federal Endangered Species Act. In fact, all three of the butterfly species in the Zerene genus are now listed as threatened or endangered under the Endangered Species Act. The Myrtle’s Silverspot is the most southernly distributed of these three species, but today it is found in only four known locations, all outside of the GGNP. However, because the species naturally has wide population swings—sometimes an order of magnitude in size or more in a single year—it is very difficult to declare definitively that the species has been lost without extensive surveys. Moreover, recovery efforts will require reestablishing the species in former habitat areas, and the GGNP may be essential to that effort.

Conservation Action Item

Reintroduce Populations:
Encourage Reintroduction of the Myrtle's

Habitat loss and degradation is the main threat to species survival. In order to save the species from extinction, existing populations must be connected with habitat corridors and old populations sites need to be reestablished in a vigorous recovery campaign. The GGNP is currently considering a reintroduction program within the Park’s San Mateo County lands. Encourage the GGNP to reintroduce the Myrtle’s Silverspot Butterfly in its former habitats by asking your public officials to fund butterfly conservation and reintroduction efforts.

Big Year Competitors have reported 0 sightings and taken 2 actions to help this species recover so far this year.

Trips

• None scheduled