San Bruno Elfin Butterfly (Lepidoptera: Lycaenidae)

Scientific Name: Incisalia mossii bayensis
Date of listing: 1976
Federal Status: Endangered
State Status: None

The San Bruno Elfin Butterfly inhabits rocky outcrops and cliffs in coastal scrub on the San Francisco peninsula. Its patchy distribution reflects that of its host plant, stonecrop (Sedum spathulifolium). Adults of this butterfly emerge in early spring, in February and March, when flowers which provide their nectar diet begin to open. They mate soon thereafter and the female must locate appropriate host plants on which to deposit her eggs. The eggs typically hatch within a week. The tiny larvae first feed on the plant's vegetative structures. However, when the stonecrop's flowers begin to open the larvae migrate upward and feed on the flowers themselves. By June most have completed their larval development, at which time they leave the host plant to pupate in ground litter. They lie dormant as pupae until the following spring, when the cycle begins again.

An interesting aspect of this butterfly's life cycle (one common to many lycaenids) is its mutualistic interaction with ants. Elfin larvae excrete a sweet liquid known as honeydew which attracts ants. In exchange for honeydew, the ants often provide protection from harm by predators and parasites, major mortality factors in foliage feeding insects.

The San Bruno Elfin is restricted to a few small populations, the largest of which occurs on San Bruno Mountain. Its habitat has been diminished in the past by quarrying, off-road recreation, and urban development. Development pressures on the San Francisco peninsula continue to grow. To protect this as well as the Mission Blue Butterfly a unique habitat management plan has been implemented on San Bruno Mountain, in which the lower slopes were opened for development while the higher areas were converted to public ownership as critical habitat.

Current management on San Bruno Mountain and in other areas focuses on reduced pesticide use, careful recreation management, and vegetation management. Several areas from which populations had been previously extirpated are also being targeted for revegetation and reintroduction of the butterfly.

For further reading:
Brown, R.M., 1969. Larva and habitat of Callophrys fotis bayensis. Journal of Research on the Lepidoptera 8: 49-50.

Emmel, J.F. and C.D. Ferris, 1972. The biology of Callophrys (Incisalia) fotis bayensis (Lycaenidae). Journal of the Lepidopterist's Society 26 (4): 237-244.