The San Bruno Elfin Butterfly was protected by the Endangered Species Act on June 1, 1976. Only an inch-wide, the species was overlooked by lepidopterists until 1968 when it was finally described. It is endemic to foggy cliff edges and rocky outcrops on steep, north-facing slopes. The butterfly’s host plant is stonecrop (Sedum spathulifolium), a species endemic to coastal scrub communities.

Adults emerge from pupae from late February to mid-April, with a peak in late March. The females lay eggs on stonecrop leaves, and 3-7 days later red or yellow larvae that blend-in with the reddish bracts and yellow flowers of the host plant hatch and begin to feed. When the plant begins to bloom, the larvae creep up the stalks and dine on flower heads; around this time, they also secrete a sweet liquid known as honeydew that attracts ants. Scientists believe that the ants help protect the larvae from predators and parasites.

In June, the larvae have matured and they descend to the ground and pupate in leaf litter. They lie dormant until the following February or March. At the end of this stage, new adults emerge, starting the cycle of life over again.

The major remaining population of this species exists on its namesake, San Bruno Mountain. However, you can still find the species in the GGNP: an additional population clings to existence on Milagra Ridge, in San Mateo County.

Conservation Action Item

Restore Elfin habitat:
Volunteer at San Bruno Mountain and/or in Pacifica

The San Bruno Elfin Butterfly persists despite a variety of threats that impact the species’ limited habitats. Improving existing habitats and restoring others will be key to the species’ long-term survival. Volunteer to restore San Bruno Elfin Butterfly habitats at Milagra Ridge &/or on San Bruno Mountain.

Links:

Big Year Competitors have reported 0 sightings and taken 3 actions to help this species recover so far this year.

Trips

Habitat Restoration for Mission Blue and San Bruno Elfin Butterflies
Saturday, 27 Mar 2010, 10:00 - 13:00 Pacific Time (US & Canada)

Comments

Liam O'Brien — 17 August 2010 - 16:39

In June of this year, Christina Crocker reported the highest number of larvae of this creature ever found on Milagra Ridge feeding on the flower heads of the Sedum — it’s host. I went with a group in May and did not see any, but this news from Christina is wonderful considering that population was once considered extripated…

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