Scientists are making a second attempt to return a threatened butterfly to a park it used to call home.
More than three years ago, Christal Niederer and other researchers tried to reintroduce the Bay checkerspot butterfly to the rolling hills of Edgewood Park, just east of Interstate 280.
But the April 2007 introduction of about 1,000 caterpillars didn’t take. By winter 2008, officials found one checkerspot larva and no adults. A year later, they found no checkerspots at all, and “we looked pretty hard,” Niederer said.
While they don’t know for certain, scientists suspect a dry winter after the reintroduction choked out the dwarf plantain, the preferred food of the butterflies’ larvae.
Now, backed by a determined volunteer-supported effort to remove invasive plants in the butterfly habitat, they are hoping to bring a new colony of caterpillars to the 467-acre park this spring.
Niederer said they are hoping for a boom in the largest remaining checkerspot population, at Coyote Ridge near San Jose, which is where the caterpillars for Edgewood would come from. She said the butterfly habitat at Edgewood “looked fantastic” earlier this year.
“It looks like everything they should want, so we want to try again and see what happens,” said Niederer, a biologist with the Menlo Park-based Creekside Center for Earth Observation, which is heading the project.
The butterfly’s population at Edgewood declined precipitously in the late 1990s, until it vanished completely by 2003.
Scientists suspect non-native invasive species like the Italian ryegrass crowded out native plants that supported the butterflies.
The conservationists believe pollution from the nearby highway enriched the serpentine soil with nitrogen, fueling ryegrass growth.
The grass also forms a thick yellow-brown thatch on top of the soil that prevents the wildflowers that adult butterflies use for food from thriving.
Recently, San Mateo County Ranger John Trewin hooked up a new metal “de-thatcher” resembling a chain-link fence to drag behind his off-road tractor.
“This should bust it up a little bit,” Trewin said.
Niederer estimated that it costs about $5,000 per month to maintain the butterfly habitat, including de-thatching and periodic mowing. The restoration project is funded by grants from a variety of sources, including the U.S. Fish and Wildlife Service, PG&E and Friends of Edgewood.
“Mother Nature, she just can’t restore herself without a little help,” said Julia Bott, executive director of the San Mateo County Parks Foundation.
Bringing back a species
1987: The Bay checkerspot butterfly is listed as threatened under the federal Endangered Species Act, giving it legal protection
1993: Edgewood is officially designated as a natural preserve
1995: About 5,000 butterflies hold on at Edgewood
1998: The Edgewood checkerspot population begins sharp decline
2002: Single checkerspot caterpillar is found at Edgewood
2003: No checkerspots are found at Edgewood
2007: After years of habitat restoration, scientists reintroduce
1,000: Caterpillars to Edgewood
2009: Checkerspots are again nowhere to be found at Edgewood
Source: Friends of Edgewood
Bay checkerspot butterfly facts
Scientific name: Euphydryas editha bayensis
Wingspan: About 2 inches
Eggs: Laid in March/April in masses of between five and 250
Hatching: Caterpillars emerge in about 10 days
Habitat: 18,293 acres in Santa Clara and San Mateo counties designated as critical habitat
Source: U.S. Fish and Wildlife Service