Mission Blue Butterfly

Icaricia icarioides missionensis

Description

The mission blue butterfly, Icaricia icarioides missionensis, measures about 1-1.4 in (2.5-3.5 cm) across the wingtips. The male is silver-blue to violet-blue above, with dark wing margins; the female is completely brown above or with blue restricted to wing bases. Beneath, both sexes are silver-gray or brownish with black spots on the front wing. This species has also been referred to as Plebejus icarioides missionensis.

Behavior

Adults begin to emerge from pupae in late March and fly until mid-June. They have an average life span of 10 days. Females are fertile throughout their life, depositing single eggs on the leaves, stems, flowers, and seedpods of the host plant, one of several species of lupine. Eggs hatch in four to seven days, but the larvae overwinter in leaf litter at the base of the host plants. In spring, the larvae resume feeding, then pupate. Parasitic wasps attack and lay their eggs inside the mission blue's larvae, but often the larvae are tended by ants, which provide some protection from wasp parasites and other predators. In exchange, the larvae secrete honeydew for the ants.

Habitat

The mission blue inhabits grasslands and coastal scrub. It is also found along the borders of dunes or tidal marshes. Spring and summer climate is relatively cool, windy, and cloudy. Maximum summer temperatures average less than 70°F (21°C). Winter temperatures seldom fall below freezing (32°F, or 0°C). Three perennial lupine species serve as larval host plants (Lupinus albifrons, L. formosus, and L. variicolor ).

Distribution

The mission blue butterfly is endemic to the San Francisco peninsula and Marin County, California. This subspecies was first collected in 1937 on Twin Peaks in the Mission District of San Francisco. Except for small colonies in the Mission District of San Francisco and at Fort Baker in Marin County, other colonies of mission blue butterflies were known to occur on about 1,500 acres (600 hectares) of grassland at San Bruno Mountain south of San Francisco. Several populations were recently discovered in northern and central San Mateo County.

Threats

Loss of habitat to urban San Francisco and related residential development is the major cause for the decline of the mission blue butterfly. Its habitat has also suffered from industrial and agricultural development, quarrying, and the encroachment of non-native plant species that crowd out the lupine host plants. The Fort Baker colony near the north end of the Golden Gate Bridge is afforded protection by the Golden Gate National Recreation Area.

Conservation and Recovery

The Mission blue butterfly's host plants grow in a plant community that depends on periodic disturbances, such as rock slides, mud slides, and fires, to establish seedlings. Preserving the mission blue butterfly will require maintaining sufficient tracts of lupine, which, in turn, depends on sustaining the natural succession of vegetation by inducing periodic disturbance.

A development company, Visitacion Associates, donated 298 acres (121 hectares) of habitat on San Bruno Mountain to the San Mateo County Parks and Recreation Department. The San Bruno Mountain Habitat Conservation Plan has been developed to maintain several hundred acres of open habitat while allowing residential development to continue in other parts of the historic habitat area. The long-term outlook for the mission blue is guardedly optimistic.

Contact

U. S. Fish and Wildlife Service
Regional Office, Division of Endangered Species
Eastside Federal Complex
911 N. E. 11th Ave.
Portland, Oregon 97232-4181
Telephone: (503) 231-6121
http://pacific.fws.gov/

References

Arnold, R. A. 1983. "Ecological Studies of Six Endangered Butterflies (Lepidoptera: Lycaenidae): Island Biogeography, Patch Dynamics, and Design of Habitat Preserves." University of California Publications in Entomology 99: 1-161.

Arnold, R. A. 1987. "The Mission Blue Butterfly." InAudubon Wildlife Report 1987. National Audubon Society, San Diego.

McClintock, E., W. Knight, and N. Fahy. 1968. "AFlora of the San Bruno Mountains, San Mateo County, California." Proceedings of the California Academy of Science 32: 587-677.

San Bruno Mountain Habitat Conservation PlanSteering Committee. 1982. "San Bruno Mountain Area Habitat Conservation Plan." San Mateo County Planning Department, Redwood City, Calif.

U.S. Fish and Wildlife Service. 1984. "Recovery Plan for the San Bruno Elfin and Mission Blue Butterflies." U. S. Fish and Wildlife Service, Portland, Oregon.