U.S. Fish & Wildlife Service

Sacramento Fish & Wildlife OfficeServing the people, conserving the fish, wildlife, and plants of California

A Unit Of The Pacific Southwest Region

Species Information

Photo of Bay Checkerspot Butterfly

Photo Credit: Steve Martarano / USFWS

Bay Checkerspot Butterfly

Euphydryas editha bayensis

Basic Species Information


Threatened. The species is likely to become endangered in the foreseeable future throughout all or a significant portion of its range, but they are not in danger of extinction right now.


The bay checkerspot is a medium-sized butterfly in the brush-footed butterfly family (Nymphalidae). It has a wing span of little more than 5 cm (about 2 inches). The forewings have black bands along all the veins on the upper surface, contrasting sharply with bright red, yellow and white spots.


The caterpillars (larvae) eat dwarf plantain and purple owl's clover. The adults feed on the nectar of their host plant.


All habitat for the bay checkerspot butterfly exists on shallow, serpentine-derived soil (i.e., high in magnesium and heavy metals and low in nutrients such as nitrogen, phosphorus and calcium). The primary larvae host plant is dwarf plantain (Plantago erecta). The larvae require a second host plant when the plantain dries up. Under these conditions, the larvae move to purple owl's clover (Castilleja densiflora or C. exserta), which remains edible later in the season.


Generally, one season is not sufficient for completion of development and the larvae must enter dormancy until the following winter when the rains allow plant growth to begin again.


Caterpillars turn into butterflies.

Adults can be seen flying around from about late February to early May. Each of them only lives about 10 days.

Males emerge about 4 to 8 days before females. Soon after the females emerge, they mate. Males can mate many times, while most females mate only once.

Eggs are typically laid in March and April. Females lay up to five egg masses of 5 to 250 eggs. The eggs are laid at the base of plantain, owl's clover or paintbrush.

Caterpillars hatch from the eggs in about 10 days. They grow for 2 weeks or more, shedding their skin three times. Then they rest during the summer. (This phase is called diapause. It is sort of like hibernation.)

When the rainy season comes, the caterpillars become active again. Then they spend the winter in a shell called a chrysalis (like a cocoon). This is called the pupa stage.


Historically, the Bay checkerspot occurred primarily along the spine of the San Francisco peninsula, from Twin Peaks to southern Santa Clara County and in a few pockets in Alameda and Contra Costa counties. However, habitat loss and fragmentation, extreme weather, air pollution, pesticides, vehicle strikes, fire, overgrazing, gopher control, illegal collecting, and invasion of exotic species have greatly reduced the butterfly's numbers. See the Federal Register notice for revised critical habitat for more information.


Threats include habitat loss and fragmentation, invasion of exotic/invasive plants, nitrogen deposition (including NOX and ammonia), pesticide application (including drift), illegal collecting, fire, overgrazing, and gopher control.


If you live in the San Francisco Bay, you may be able to help restore the Bay checkerspot's home. Search the Internet for Bay checkerspot butterfly volunteer. People are needed to pull weeds and plant native plants.

KQED radio station has a great web page (330 KB PDF). The page has information, lesson plans, web links and field trip ideas.

Consider planting a butterfly garden.

Last updated: April 4, 2018