Press Releases:

April 30, 2001 - U.S. Designates 23,903 Acres in San Mateo and Santa Clara Counties as ‘Critical Habitat' for Bay Checkerspot Butterfly

Imperiled Butterflies of the
San Francisco Bay Area

Bay Checkerspot Butterfly (Euphydryas editha bayensis)


Bay Area Checkerspot Butterfly © Richard A. Arnold

Butterflies not only grace our skies with their fluttering streaks of color, but as pollinators, they also play a vital role in maintaining healthy functioning of the ecosystems we depend upon, the existence of specialized plants, and a stable food supply. Unfortunately, many of the wild pollinators in North America are in decline.

The Bay Checkerspot Butterfly depends upon several native plants as host plants. These host plants 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 (found nowhere else) species.

Populations of Bay Checkerspots historically occurred in numerous areas around the San Francisco Bay including the San Francisco peninsula, the mountains near San Jose, the Oakland hills, and several spots in Alameda County. Most of these populations have been eliminated due to explosive urban development, and the butterfly has been extirpated from Contra Costa, Alameda and San Francisco Counties. Populations now remain only in San Mateo and Santa Clara Counties. Unfortunately, the majority of the checkerspot's serpentine soil habitat in San Mateo and Santa Clara Counties also has been destroyed.

The Bay Checkerspot Butterfly depends upon several different host plants during its life cycle; eggs are laid on a native plantain, which the larvae feed upon. If this food is not sufficient for development, the larvae may move onto Owl’s Clover. The larvae then generally enter dormancy until the following winter, and then emerge to feed again, pupating in late winter. Finally, the adults emerge shortly thereafter.

Bay Checkerspot Butterflies and their specialized serpentine habitat are threatened by urban development, pesticides, nitrogen deposition, global warming and air pollution. The Bay Checkerspot Butterfly was listed as a threatened species in 1987. Critical habitat for the butterfly was designated in 2001. A recovery plan for the butterfly was published in 1998.

Center Actions to Protect the Bay Checkerspot Butterfly:

• In 2001 the Fish and Wildlife Service designated 23,903 acres in San Mateo and Santa Clara Counties as critical habitat for the Bay Checkerspot Butterfly, in keeping with a legal settlement obtained by the Center.
• In 2000 the Center filed suit against the U.S. Army Corps of Engineers, challenging approval of the Ranch on Silver Creek development project near San Jose, a 575-acre golf course and luxury housing development that would have destroyed some of the best remaining habitat for the Bay Checkerspot Butterfly. The Center won a preliminary injunction halting the development and the case was settled in 2001, with the developer agreeing to reroute the golf course to preserve more butterfly habitat, to spend $1 million to manage a butterfly preserve on the land and parts of an adjacent property, and to buy 90 acres of butterfly habitat south of the project and on a ridge above Coyote Valley.
• In 1999 the Center sued the Fish and Wildlife Service to secure critical habitat for the Bay Checkerspot Butterfly.

Callippe Silverspot Butterfly (Speyeria callippe callippe)


Callippe Silverspot Butterfly © San Bruno Mountain Watch

The Callippe Silverspot Butterfly’s colors are primarily orange, tan and brown on its upper side. Silverspot butterflies are so named because of silver spots or scales on the undersides of their wings. Historically, this species inhabited native grasslands throughout much of the northern San Francisco Bay region. It is associated with the native violet Johnny Jump-up (Viola pedunculata), on which the larvae feed and the female butterflies lay their eggs.

The historic range of the Callippe Silverspot Butterfly includes the inner Coast Ranges on the eastern shore of San Francisco Bay from northwestern Contra Costa County south to the Castro Valley area in Alameda County. On the west side of the Bay, it ranged from San Francisco south to the vicinity of La Honda in San Mateo County. There were 14 known historic occurrences of the species. All of the colonies, including one located at Twin Peaks in San Francisco, have been extirpated except for those at two sites: private land on San Bruno Mountain in San Mateo County, and a city park in Alameda County.

A significant amount of destruction of Callippe Silverspot Butterfly habitat was allowed under the San Bruno Mountain Habitat Conservation Plan, the nation's first such plan. Remaining Callippe Silverspot Butterflies are threatened by development, livestock grazing, collecting and non-native plant invasions. The Callippe Silverspot Butterfly was listed as an endangered species in 1997. Critical habitat for this butterfly was proposed in 1978 and 1980, but never finalized.

Center Actions to Protect the Callippe Silverspot Butterfly:

• In 2000 the San Bruno Mountain lawsuit was settled, with the Trust for Public Land agreeing in July 2001 to purchase and protect 25 sensitive acres, including the Ohlone shell mound and habitat for the butterflies. This set-aside, supported by the Pajaro Valley Ohlone Indian Council and the South San Francisco City Council, will be added to 2,700 acres on the mountain already protected as state and county parks.
• In 1999 the Center and San Bruno Mountain Watch filed suit challenging approval of a 300-acre hotel, office park and housing at the Terra Bay Development on San Bruno Mountain that failed to consider the impacts on the endangered Callippe Silverspot and Mission Blue Butterflies and a 5,000-year-old Ohlone Indian shell mound.
• In 1998 the Center threatened to sue the Fish and Wildlife Service for failure to designate critical habitat for the Callippe Silverspot Butterfly.
• In 1997 the Fish and Wildlife Service listed the Callippe Silverspot Butterfly as endangered in response to a threatened lawsuit by the Center. The Service refused to designate critical habitat, claiming that doing so would alert collectors of its presence. This is nonsense since the critical habitat designation would be less detailed than several already available butterfly habitat maps.

Mission Blue Butterfly (Icaricia icariodes missionensis)
San Bruno Elfin Butterfly (Incisalia mosii bayensis)


Mission Blue Butterfly
© Andrew Sanchez, CA Academy of Sciences


San Bruno Elfin Butterfly © San Bruno Mountain Watch

Formerly relatively widespread throughout the San Francisco and Marin peninsulas, the Mission Blue Butterfly now remains at only a few sites in the coastal counties, primarily on San Bruno Mountain in San Mateo County. Mission Blue Butterfly larvae are dependent on perennial lupines as their host plant.

San Bruno Elfin Butterflies inhabit rocky outcrops and cliffs only in the coastal scrub on the San Francisco peninsula. The largest San Bruno Elfin Butterfly population also occurs on San Bruno Mountain. These butterflies are dependent upon stonecrop (Sedum spathulifolium) as a host plant. San Bruno Elfin Butterfly larvae have a mutualistic association with ants. The larvae excrete a sweet honeydew liquid to attract ants, which provide protection from predators and parasites.

Both butterflies are threatened by invasive plants that reduce suitable habitat for their host plants. Other threats include additional urban development on the flanks of San Bruno Mountain and pesticide use in proximity to their habitat.

The Mission Blue and San Bruno Elfin Butterflies were both listed as endangered in 1976. Critical habitat was proposed for both butterflies in 1977, but was never finalized. A recovery plan for both species was published in 1984.

Center Actions to Protect the Mission Blue and San Bruno Elfin Butterflies:

• In 2000 the San Bruno Mountain lawsuit was settled, and in July 2001 the Trust for Public Land agreed to purchase and protect 25 sensitive acres, including the Ohlone shell mound and habitat for the butterflies. This set-aside, supported by the Pajaro Valley Ohlone Indian Council and the South San Francisco City Council, will be added to 2,700 acres on the mountain already protected as state and county parks.
• In 1999 the Center and San Bruno Mountain Watch filed suit challenging approval of a 300-acre hotel, office park and housing at the Terra Bay Development on San Bruno Mountain that failed to consider the impacts on the endangered Callippe Silverspot and Mission Blue Butterflies and a 5,000-year-old Ohlone Indian shell mound.

Myrtle’s Silverspot Butterfly (Speyeria zerene myrtleae)
Behren’s Silverspot Butterfly (Speyeria zerene behrensii)


Myrtle's Silverspot Butterfly,
National Park Service


Behren's Silverspot Butterfly
U.S. Fish and Wildlife Service

Myrtle’s Silverspot Butterfly was formerly widespread on the San Francisco and Marin peninsulas, but now only four populations remain in northern coastal Marin and Sonoma counties. Former populations near Pacifica and San Mateo in San Mateo County are thought to be extirpated. The species inhabits dunes, scrub, and grasslands habitats. It is dependent upon native violets (Viola spp.) as its host and food plant. Silverspot larvae are extremely sensitive to pesticides and even can be killed by accumulation of runoff in the soil after pesticide spraying. This species is threatened by urban development, off-road vehicle use, and loss of larval food plant and adult nectar resources due to invasive plants and inappropriate levels of grazing.

Behren's Silverspot Butterfly no longer occurs in the Bay Area. Historically, it ranged from the Russian River in Sonoma County north to Point Arena in southern Mendocino County, but now remains in a single population on a coastal terrace prairie at Point Arena, in southern Mendocino County. The species is threatened by development, livestock grazing, collecting and non-native plant invasions.

The Myrtle’s Silverspot Butterfly was listed as endangered in 1992. No critical habitat has been designated. A recovery plan for the species was published in 1998. The Behren’s Silverspot Butterfly was listed as endangered in 1997. No critical habitat has been designated. A draft recovery plan for the species was published in 2004.

Center Actions to Protect the Myrtle’s and Behren’s Silverspot Butterflies:

• In 1998 the Center threatened to sue the Fish and Wildlife Service for failure to designate critical habitat for the Myrtle’s and Behren’s Silverspot Butterflies.
• In 1997 the Fish and Wildlife Service listed the Behren’s Silverspot Butterfly as endangered in response to a threatened lawsuit by the Center.

Pesticides and Butterflies

• In March 2006 the Center released a comprehensive report detailing the risk toxic pesticides pose to endangered species in the Bay Area, including the Bay Checkerspot, Mission Blue, San Bruno Elfin, Lange’s Metalmark, and Callippe, Myrtle’s and Behren’s Silverspot Butterflies.

April 6, 2007
Go back