Center for Biological Diversity

Protecting endangered species and wild places of western North America
and the Pacific through science, policy, education, and environmental law.

For Immediate Release: April 30, 2001
For More Information: Peter Galvin (707) 923-4654
More Information: Goldenstate Biodiversity Initiative



Today, the U.S. Fish & Wildlife Service (FWS) finalized the designation of 23,903 acres in San Mateo and Santa Clara Counties as ‘critical habitat' under the Endangered Species Act (ESA) for the Bay Checkerspot Butterfly. The Center filed suit against FWS in the United States District Court for the Northern District of California on June 30, 1999 for failure to designate critical habitat under the ESA. The Bay Checkerspot Butterfly was originally listed as Threatened under the ESA in 1987. Critical habitat was first proposed in the 1980's for the species but was subsequently withdrawn.

In a strongly-worded opinion issued on August 30, 2000, federal judge Samuel Conti quoted Congress to point out the connection between conserving biological diversity and human welfare: "From the most narrow possible point of view, it is in the best interests of mankind to minimize the losses of genetic variations....who knows, or can say, what potential cures for cancer or other scourges...may lie locked up in the structures of plants which may yet be undiscovered, much less analyzed?"

Judge Conti ordered the FWS to complete the designation process for the Bay Checkerspot Butterfly within 120 days.
Critical habitat includes all areas necessary for the survival and full recovery of the species. It is protected from federal projects for permits which would destroy or adversely modify the habitat.

"Peter Galvin, California Director for the Center for Biological Diversity stated "The Bay Checkerspot Butterfly is one of California's most beautiful and magnificent creatures. We are hopeful that today's habitat designation will help turn the tide toward recovery for the species."

The Bay Checkerspot Butterfly depends on host plants which grow primarily in grasslands on serpentine soils, a bluish-green soil type that is naturally highly mineralized, high in magnesium, and low in nitrogen and calcium. This specialized soil system is very valuable biologically because it supports a high percentage of California's endemic species. Unfortunately, the majority of the Checkerspot's serpentine soil habitat in the Bay area has been destroyed.
The Center for Biological Diversity is a science-based environmental advocacy organization. The Center was founded in 1989, and has more than 6,000 members. In California, the Center has offices in Berkeley and San Diego. The Center works to protect endangered species and wild places throughout western North America and the Pacific through science, policy, education and environmental law.

To view a photograph of the Bay Checkerspot Butterfly or to the complete text of the critical habitat designation.


The Bay Checkerspot is a medium-sized butterfly with a wingspan of about 2 inches. The forewings have black bands along all the veins on the upper wing surface, contrasting sharply with bright red, yellow, and white spots.

The Bay Checkerspot formerly occurred around San Francisco Bay, from Twin Peaks and San Bruno Mountain (west of the Bay) and Contra Costa County (east of the Bay) south through Santa Clara County.

Adult Bay Checkerspot Butterflies are capable of dispersing over long distances. Movements of more than 3.5 miles have been documented

The decline of the Bay Checkerspot is primarily attributed to loss of habitat and fragmentation of habitat due to increasing urbanization. Drought and other extremes of weather have also been implicated in bay Checkerspot population declines Recent research has identified excess nitrogen deposition from polluted air as a threat to bay Checkerspot habitats, due to its fertilizing effect enhancing the growth of invasive nonnative plants even in serpentine soil areas.

The known range of the Bay Checkerspot is now reduced to Santa Clara and San Mateo Counties, and the butterfly is patchily distributed in these locales.


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