Bay Checkerspot Butterfly

Euphydryas editha bayensis


Photo by: Richard A. Arnold

Photo by: Richard A. Arnold

Populations of the bay checkerspot historically inhabited 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, but populations have experienced serious declines since the mid-1980s. Because this species has been extensively studied its decline was quickly identified, prompting its listing as threatened in 1987. Threats include destruction and fragmentation of habitat due to urban and suburban sprawl, invasion of nonnative plants, inappropriate management grazing and fire, and extreme weather.


The bay checkerspot (Euphydryas editha bayensis) is a medium-sized butterfly in the brush-footed butterfly family (Nymphalidae). It has a wing span of a little more than 2 inches. The dorsal surfaces of the wings have black bands along all the veins on the surfaces, contrasting sharply with bright red, yellow and white spots.

Life History

All habitats for the bay checkerspot exist on shallow, serpentine-derived or similar soils. These soils support the plants on which the caterpillars (larvae) feed. The primary larval host plant is dwarf plantain (Plantago erecta). In many years, the larvae require a second host plant when the plantain dries up, purple owl’s clover or paintbrush, which remains edible later in the season.

Adults emerge in early spring. They feed on nectar, mate, and lay eggs during a flight season that typically lasts for four to six weeks between late February and early May. Males typically emerge four to eight days before females. Males can mate many times, while most females mate only once. The average life span for adults is about ten days. Eggs are typically laid in March and April. Females lay up to five egg masses of 5 to 250 eggs each, which they deposit near the base of the plantain, or, when dry conditions necessitate, the owl’s clover or paintbrush. Larvae hatch from the eggs in about ten days. They grow for two weeks or more, shedding their skin three times.

Larvae that successfully reach the fourth instar enter a period of dormancy that lasts through the summer. They pass this time under rocks or in cracks in the soil. The diapause ends with the onset of the next rainy season and the germination of dwarf plantain. The larvae then resume activity, feeding and completing their development.


Historically, the bay checkerspot occurred east, west, and south of San Francisco Bay, from Twin Peaks in San Francisco and Mount Diablo in Contra Costa County south approximately to Hollister. Before the introduction of invasive Eurasian grasses and other weeds, which have reduced the abundance and distribution of its host plants, the distribution may have been wider.

Currently, the range is much reduced and patchy. There are six known core areas-one on the San Francisco peninsula, one in San Mateo County, and four in Santa Clara County. However, any site with appropriate habitat within the historic range should be considered potentially occupied.

Conservation Status

Critical habitat was designated April 2001. 1999 and 2000 reconnaissance suggests the total population size is similar to 1998. No new information in 2001 supporting change in status.

Conservation Needs

Necessary recovery actions include restricting collection of the butterfly, monitoring known populations and searching for new ones, and continuing data collection to determine if there are any other threats to the species.

Working with landowners

In Santa Clara County much of the butterfly’s habitat is on property owned by a landfill corporation. An agreement worked out among the owner, the city of San Jose, and conservation advocates has resulted in the protection of much of this habitat in exchange for permitted, conscientious development of a small portion of it. In addition, the landowner has provided funding for the establishment of a butterfly preserve and for research towards successful management of the bay checkerspot.


Education sheets available at zoological facilities (e.g. zoos, aquariums, botanical gardens with butterflies, butterfly houses, natural history museums) or events at which BFCI partners participate are a valuable way to disseminate information about imperiled butterflies.

When schools and other youth organizations study biodiversity and species extinctions they typically use examples of charismatic megafauna (e.g. bald eagles) or exotic creatures from the tropics. However, vulnerable species found within the state or ecoregion in which students live provide an excellent opportunity to develop curricular materials with a direct link to the students’ home region. In addition to classroom studies, students may be able to visit sites to see the butterflies, as well as talk to the scientists and land managers involved in the species’ conservation.

Educational activities that school students and community members could do include:

  • studying butterfly (insect) life stages;
  • researching the special habitat needs of the bay checkerspot;
  • corresponding or meeting with the biologists managing current bay checkerspot sites;
  • visiting bay checkerspot sites during adult flight season;
  • visiting captive breeding programs;
  • assisting scientists with on-site habitat management;
  • propagating and growing host plants for planting at butterfly sites or use in captive breeding programs; and
  • writing letters to decision makers to ensure that the bay checkerspot receives adequate resources and protection.


Information was not available at the time of publication.

Captive Rearing

Information was not available at time of publication.

Recovery Plan

Serpentine Soil Species of the San Francisco Bay Area (25.3MB pdf), September 30, 1998.

More Info

  • USFWS Contact: Don Hankins, Sacramento Fish and Wildlife Office, 2800 Cottage Way, Room W-2605, Sacramento, California 95825, Phone (916) 414-6600.
  • Entomological Consulting Services, Ltd.: Richard Arnold, 104 Mountain View Court, Pleasant Hill, California 94523-2188, Phone (925) 825-3784.


  • Murphy, D.D., 1988. Ecology, politics and the Bay Checkerspot butterfly. Wings 13(1): 4-8, 15.
  • Murphy, D.D., 1988. The Kirby Canyon Conservation Agreement: A model for the resolution of land-use conflicts involving threatened invertebrates. Environmental Conservation 15(1): 45-48.
  • Murphy, D.D. and S.B. Weiss, 1988. Ecological studies and the conservation of the Bay Checkerspot butterfly, Euphydryas editha bayensis. Biological Conservation 46(3): 183-200.
  • Thelander, C. ed. 1994. Life on the edge: a guide to California’s endangered natural resources. BioSystem Books. Santa Cruz, CA. pp. 438-439.
  • U.C. Berkeley, Essig Museum of Entomology. California’s Endangered Insects Bay Checkerspot page.
  • U.S. Fish and Wildlife Service. 1998. Recovery Plan for Serpentine Soil Species of the San Francisco Bay Area (in PDF). Portland, Oregon.

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