Nature Notes: Save a Home for the Bay Checkerspot Butterfly!


by Sutapa Biswas, Teaching Intern

Last semester when I took my Entomology class, I heard about the Bay Checkerspot Butterfly for the first time. I learned that the Bay Checkerspot population was once distributed around the bay in San Francisco, Santa Clara, San Mateo, Alameda, and Contra Costa counties. I was very surprised to hear that now we can see them in San Mateo and Santa Clara Counties only.

The Bay Checkerspot Butterfly is a medium-sized butterfly and is marked with black bands. The bands contrast sharply with bright red, yellow, and white spots. This black banding gives the Bay Checkerspot its unique appearance and its name. It emerges as a butterfly typically in March and April. The larvae are dependent on the host plants, mostly the dwarf plantain, whereas the adult butterflies live on nectar. The habitat for the Bay Checkerspot Butterfly consists of shallow, serpentine soils. These serpentine soils support the plants on which the caterpillars feed, like California goldfields.

In particular, this butterfly has experienced serious decline in its population since 1987 and has been listed as a threatened species. Threats include loss and fragmentation of habitat due to urbanization and degradation of habitat by invasive species, poor land management, grazing, and non-prescribed fires. Increased nitrogen deposition associated with air pollution is increasing the fertility of serpentine soils, which are naturally low in nitrogen, and allowing exotic grasses to invade the butterfly’s habitat crowding out the Bay Checkerspot’s host plants.

Recent studies have shown that existing populations are limited to Coyote Ridge between San Jose and Gilroy because it consists of serpentine habitat. More recently, scientist Stuart Weiss released 400 Bay Checkerspot caterpillars into Edgewood County Park and Natural Preserve in Redwood City with the help of volunteers.

I was lucky enough to see them in Coyote Ridge when I went there to help one of my friends with her project. There are new docent programs that began this year, a joint project of the Silicon Valley Land Conservancy, the California Native Plant Society, and the Santa Clara County Open Space Authority. So if we want, we can save our very own Bay Checkerspot Butterfly through habitat restoration and management.

Photo credit: John Cleckler


Additional Resources:

University of California at Berkeley; Essig Museum of Entomology: California’s Endangered Insects, Bay Checkerspot (Accessed 3/23/05)