Bay Checkerspot Butterfly


Description and biology

The bay checkerspot butterfly is a medium–sized butterfly with a maximum wingspan of 2.25 inches (5.72 centimeters). Females are slightly larger than males. The butterfly’s black upper surface is checkered with bright red and yellow markings. Its yellow underside has sharp black and red patterns.

The life cycle of a bay checkerspot butterfly takes about a year to complete. The insect undergoes four stages: egg, larva, pupa (cocoon), and adult. This four–stage cycle is referred to as a complete metamorphosis (pronounced met–a–MORE–fa–sis) or change.

After mating in early spring, females lay eggs on host plants in batches of 20 to 95. Some females may lay as many as 1,200 eggs in a season, but the normal maximum is 600 to 700.

The eggs soon hatch and the larvae or caterpillars begin feeding on their host plants. By late summer, if the larvae have developed enough or if the plants have begun to dry up from the summer heat, the larvae enter a dormant or resting stage.

When winter rains revive the dry plants, the larvae become active again. In late winter, they enter the pupal, or cocoon, stage, transforming in two weeks into adult bay checkerspot butterflies. The adults feed on the nectar of several plants.

Habitat and current distribution

Bay checkerspot butterflies are known to exist only in San Mateo and Santa Clara counties in California. Because the number of butterflies alive each year changes dramatically, the total population size has never been estimated.

This butterfly inhabits grasslands where species of plantain and owl’s clover—the butterfly’s host plants—grow in high numbers.


History and conservation measures

Bay checkerspot butterflies once 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.

All of these habitat areas were lost as urban development exploded in the region in the twentieth century. The butterflies are currently threatened with the loss of their host plants to animal grazing, brush fires, and introduced grassland plants.

In Santa Clara County, much of the remaining butterfly habitat is on property owned by a landfill corporation. An agreement between the corporation, the San Jose city government, and conservationists (people protecting the natural world) established a butterfly preserve on the property. Other habitat areas are currently being managed to provide protection for the bay checkerspot butterfly.

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