Bay checkerspot butterflies were once much more widespread throughout the SF Bay Area. Many factors, including loss of habitat and host plants (Plantago erecta), have contributed to the local extirpation of the species in many sites. Coyote Ridge is the exception, where a large, healthy population can still be found. This spring, Creekside Science estimated nearly 800,000 Bay checkerspot larvae on the the ridge.
San Bruno Mountain is one site where Bay checkerspots were once common, but were then locally extirpated. For the past four years, Creekside Science has been working on bringing this population back. This February/March, armed with a team of volunteers to help collect caterpillars, we brought Bay checkerspot caterpillars from Coyote Ridge to San Bruno Mountain, and dispersed them onto good habitat. The interesting thing about habitat at San Bruno Mountain, though, is that we are seeing the caterpillars happily utilizing a new, much more common host plant, which we believe will increase their chance of persisting on San Bruno. Plantago lanceolata, a weedy invasive plant that is closely related to their host plant seems to also work well as a host plant, so these butterflies will have much more potential habitat than if they relied solely on the dwindled patches of Plantago erecta. This year we translocated 3,859 caterpillars, which we hope will be happy in their new home!