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Golden Gate National Recreation Area

Bay Checkerspot Butterfly

Bay Checkerspot Butterfly
Euphydryas editha bayensis

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Bay Checkerspot Butterfly
Euphydryas editha bayensis

The Bay Checkerspot Butterfly is a medium-sized butterfly that flies in the Bay Area between mid-March and mid-April, just as the rainy season comes to a close.   The Bay Checkerspot is connected to a very specific habitat: grasslands associated with outcrops of serpentine.  When the caterpillars hatch, they must eat rapidly to outpace the ensuing dryness.  In a typical year, only 1-2% of the insects survive this race.

Those who do survive go dormant as soon as the last food plants dry up, and don’t emerge until late December or January with the winter rains.  After a second feasting, the caterpillars pupate, creating a cream-and-black colored pupal case.  In the spring they emerge as butterflies, wings colored like stained-glass: a patchwork of orange, yellow, and red panels edged in gray black.  After mating, the females lay their eggs on native plantain (Plantago erecta) and in an abundant year will move over to two types of owl's clover (Castilleja densiflorus and C. exserta) to begin the cycle anew.Bay Checkerspot Butterfly Hike

The Bay Checkerspot was once distributed around the Bay Area, with populations in Santa Clara, San Mateo, Alameda, Contra Costa, and even San Francisco Counties.  Today only San Mateo and Santa Clara Counties still host the species.  Rampant development, grazing, invasive plants, and catastrophic events have all played a roll in the species demise.  Indeed, from 1981 through 1987, the population at Edgewood Park—a San Mateo park that is partially within the legislative boundary of the GGNRA—saw its population of Bay Checkerspot Butterflies decline from about 100,000 in 1981 individuals to about 500 in 1987.  This prompted the U.S. Fish and Wildlife Service to protect the species as “threatened” under the federal Endangered Species Act in 1987.  

Unfortunately the population at Edgewood Park was eventually lost entirely.  It is believed that nitrogen in automobile exhaust from cars zooming by Edgewood Park on Interstate 280 was deposited in Edgewood's serpentine soils, which provided an advantage to nonnative grasses that crowded out the Bay Checkerspot's host plants.

In February of 2007, Stuart Weiss reintroduced this once-common species to Edgewood Park in San Mateo County on a grand scale: over 1,000 caterpillars gathered from another portion of the species' range were reintroduced to Edgewood Park.  To ensure that the species isn't lost again, the area is carefully mowed at specific times to keep the invasive weeds from thriving. Edgewood Park remains one of the few places to try and see this vanishing species.

Conservation Action Item

In recent years, yet another threat to the Bay Checkerspot’s continued existence has been discovered:  global warming.  It is believed that global warming will affect the growing season of the butterfly’s host plants, making it more difficult for the species to find food as it emerges from its eggs.  Do your part to combat global warming:  calculate your carbon footprint, and then reduce it.

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