Speyeria zerene behrensii
| Myrtle's silverspot | |
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| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Insecta |
| Order: | Lepidoptera |
| Family: | Nymphalidae |
| Genus: | Speyeria |
| Species: | S. zerene |
| Subspecies: | S. z. myrtleae |
| Trinomial name | |
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Speyeria zerene myrtleae Dos Passos & Grey, 1945 |
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Myrtle's silverspot (Speyeria zerene myrtleae) is a medium-sized butterfly in the brush foot family (Nymphalidae), an endangered subspecies of the zerene fritillary. It is endemic to California, where it is known from only about four locations just north of the San Francisco Bay Area, including two at Point Reyes National Seashore. Its wingspan is approximately 2.2 inches (56 mm). The upper surfaces of the wings are golden brown with numerous black spots and lines. The undersides are brown, orange and tan with black lines and silver and black spots. Larvae are dark colored with many sharp branching spines on their backs. Myrtle's silverspot is larger and paler than the closely related Behrens' silverspot (Speyeria zerene behrensii), which is now limited to the vicinity of Point Arena in Mendocino County.
The female lays a single brood of eggs in the dried herbage of violets, especially western dog violet (Viola adunca), the only known larval food plant. Upon hatching, the caterpillars wander a short distance and spin silk pads upon which they pass the winter. The larvae immediately seek out the food plant at the end of their diapause in the spring. After 7 to 10 weeks each larva pupates within a chamber of leaves it glues together with silk. Adults may emerge in about 2 weeks and can live for 3 weeks. The adult flight season may range from late June to early September. Adults feed on nectar from flowers including gumplants (Grindelia spp.), yellow sand verbena (Abronia latifolia), coyote mints (Monardella spp., especially M. undulata),bull thistle (Cirsium vulgare) and seaside daisy (Erigeron glaucus).
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