San Bruno Elfin Butterfly

Callophrys mossii bayensis

Description

The San Bruno elfin, Callophrys mossii bayensis, is a diminutive butterfly with brown upperside front wings, and undersides that are patterned with gray or dark brown. The head, crown, and front have reddish-brown scaling; the eyes are hairy and bordered with white scales; the labial palpi have mixed black and white scales. The thorax and abdomen are hairy, and concolorus with the dorsal wing surface. The hind wings are without tails.

Behavior

The San Bruno elfin produces one brood per generation. Adults emerge from pupae late February to mid-April, with a peak in late March. Males and females are able to mate soon after emergence. When a male encounters a receptive female, he releases a phermone that may lead to mating. Both sexes may mate more than once. The female deposits several dozen eggs per day for the duration of her lifetime (about one week) on the foliage of the larval host plant. The larvae hatch in five to seven days. By the time the host plant blooms, third instar (stage) larvae crawl up the flowering stalks and feed on the flowerheads. Third and fourth instar larvae are tended by ants. The larvae secrete a honeydew substance, which the ants take in exchange for protecting the larvae from predators. Pupation occurs around the base of the host plant and lasts from June until the following March. While larvae are associated exclusively with the liveforever host, adults consume nectar from the limited number of available inflorescences of other species during the early spring flight period. Males also perch on surrounding vegetation to facilitate mating. However, mating itself occurs on or immediately around liveforever (Sedum spathulifolium ), and females deposit eggs only on liveforever leaves.

Habitat

San Bruno elfin butterflies are found in a mountainous area with a grassy ground cover. The mountain side supports scattered patches of coastal scrub and woodlands and is crossed by several intermittent streams. The San Bruno elfin butterfly's larval host plants are liveforever (S. spathulifolium ) and stonecrop. Liveforever tend to occur in shallow soils, particularly on weathered, rocky substrates where chaparral cover is reduced. The cover and shelter requirements of the butterfly are supplied by the succulent leaves of the live-forever where early instar larvae bore, on the flowers where later instar larvae feed, and among the detritus at the base of the plant where pupation occurs.

Distribution

The historic range of this butterfly probably encompassed hilltops and ridges from northern San Mateo County, California, to the San Francisco Peninsula and northward into Marin County.

San Bruno Mountain, the major population site for the San Bruno elfin butterfly, is immediately south of the city of San Francisco in San Mateo County and is the northernmost extension of the Santa Cruz Mountains. The habitat is bordered by South San Francisco on the south, Brisbane on the east, Colma on the southwest, and Daly City on the north. The mountain encompasses about 3,620 acres (1,465 hectares), about half of which is owned by the San Mateo County Parks and Recreation Department. Smaller parcels are owned by the California State Parks Foundation and by Visitacion Associates, a development company.

Additional, small populations of San Bruno elfin butterfly occur at Milagra Ridge, southwest of San Bruno Mountain adjacent to the city of Pacifica, and further south at Montara Mountain, Whiting Ridge, and Peak Mountain, adjacent to the city of Montara. No recent population figures are available, although quarrying recently wiped out a major population.

Threats

Continuing urbanization in the San Francisco Bay area threatens to reduce the San Bruno elfin butter-fly's aleady limited habitat. A major portion of its remaining habitat has been under private ownership since the late 1800s. The habitat has been disturbed by road and utility-line construction, rock and sand quarrying, livestock grazing, invasion of exotic species, and water diversion.

Grazing and frequent grassfires have encouraged the growth of many introduced plants in the grasslands and reduced the coastal scrub. The permit for the existing rock quarry expired during the mid-1990s and was closed at that time subject to renewal.

The host plant of the San Bruno elfin butterfly is a persistent perennial but its rate of increase is slow. Furthermore, it only attains a competitive advantage over other plants under restricted environmental conditions that depend upon rocky outcrops and steep, extremely weathered slopes on nutrient-poor substrates. Natural disasters, such as landslides and wildfires help Sedrum and create the potential for new habitat for both the plant and the butterfly.

Conservation and Recovery

In the early 1980s a Habitat Conservation Plan was developed to allow private and public development on the mountain while minimizing the adverse effects on endangered species. The plan's goal is the long-term preservation of all rare species within the area. In the meantime, the U. S. Fish and Wildlife Service Recovery Plan recommends a program to minimize the use of herbicides and other toxic substances, to remove non-native plants, and to reestablish native plants, especially the host plant of the San Bruno elfin butterfly.

Contact

Regional Office of Endangered Species
U.S. Fish and Wildlife Service
911 N.E. 11th Ave.
Portland, Oregon 97232
http://pacific.fws.gov/

References

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

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

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.