Palos Verdes Blue Butterfly

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Palos Verdes Blue Butterfly

Glaucopsyche lygdamus palosverdesensis

Status Endangered
Listed July 2, 1980
Family Lycaenidae (Gossamer-winged butterfly)
Description Small, silvery blue with narrow black wing margins.
Habitat Cool, fog-shrouded slopes.
Host Plant Locoweed, rattlepod, and deerweed.
Reproduction Adults emerge during February and March.
Threats Urbanization, low numbers.
Range California


The Palos Verdes blue butterfly, Glaucopsyche lygdamus palosverdesensis, is a small lycaenid butterfly with a wingspan of about 1 in (25 mm). It belongs to a species commonly called the "silvery blue butterfly" because of its color. Both sexes are pale gray to dark brownish-gray below, with narrow black margins in the male and diffuse wide dark margins in the female. The Palos Verdes blue is similar in appearance to the common blue and the Reakirt's blue.


Until the 1994 discovery of a new population of Palos Verdes blue butterflies, entomologists believed the insect used rattlepod (Astragalus trichopodus var. lonchus ) exclusively as the larval host plant during reproduction. Females have since been found to deposit their eggs on the flowers and fruits of deerweed (Lotus scoparius ) as well. Caterpillars (larvae) hatch from eggs in seven to 10 days and begin feeding on the host plant. Near the end of their larval stage, Palos Verdes blue caterpillars may be tended by ants. The larvae of other G. lygdamus sub-species secrete a sugary substance that is eaten by the ants. In return, the ants may protect the caterpillars from predators and parasitoids. Adults emerge during February and March and live for an average of only four days.


The Palos Verdes blue's larval host plant, the locoweed, grows on well-drained clay or gravelly soils and is frequently found on rocky slopes, especially along the coast.


This species is restricted to the cool, fog-shrouded, seaward side of the Palos Verdes Hills in Los Angeles County, California. The foodplant occurs as far north as Santa Barbara. Until 1994, the species was known to exist only in a single population, which occupied a large vacant lot near the intersection of Los Verdes Drive and Hawthorne Boulevard in Los Angeles. This site was subsequently cleared for a housing development. Several smaller colonies were discovered nearby, but the status of the species was in doubt, and some experts feared it was already extinct. However, on March 10, 1994, U.S. Fish and Wildlife Service (FWS) biologist Dr. Rudi Mattoni rediscovered the Palos Verdes blue butterfly on the grounds of a Department of Defense facility in San Pedro, California, while conducting a survey for ground-dwelling insects. Following the butterfly's rediscovery, FWS entomologists made several additional butterfly sightings outside the Defense facility. The population is estimated to number 200 butterflies.


Urbanization has been the main cause of decline of the Palos Verdes blue butterfly. The city and suburbs of Los Angeles have expanded to encompass the butterfly's entire historic range. Weed control practices have all but eliminated the locoweed in and around the city. At remnant habitat sites, the Palos Verdes blue must compete with the more common Western tailed blue butterfly, which also feeds on the locoweed.

Conservation and Recovery

The three small habitat areas on the Palos Verdes Peninsula, where the butterfly was last seen before the 1994 sighting at the Department of Defense facility, have been designated as Critical Habitat: Agua Amarga Canyon; Frank Hesse Park; and a section along Palos Verdes Drive in the city of Rancho Palos Verdes.The Palos Verdes blue population rediscovered by Dr. Mattoni was located in an area proposed for a pipeline project. The coastal California gnatcatcher (Polioptila californica californica ), a threatened bird, also occurs in this region. The Department of Defense currently is working with FWS biologists to develop strategies to conserve both the Palos Verdes blue butterfly and the coastal California gnat-catcher. In addition, Chevron has provided funding for Dr. Mattoni to sample vegetation in the pipeline area in order to determine its suitability for recolonization by these unique species.


Regional Office of Endangered Species
U.S. Fish and Wildlife Service
911 N.E. 11th Ave.
Portland, Oregon 97232


Arnold, R. A. 1980. "Status of Proposed Threatened or Endangered California Lepidoptera." Contract Report to California Department of Fish and Game, Sacramento.

Arnold, R. A. 1987. "Decline of the Endangered Palos Verdes Blue Butterfly in California." Biological Conservation 40(1987):203-217

Mattoni, R. H. T. 1994. "Current Status of the PalosVerdes Blue Butterfly at the U. S. Navy Fuel Storage Reserve, San Pedro, California." Agresearch Inc. report prepared for Chevron Oil.

Mattoni, R. H. T. 1993. "The Palos Verdes blue, Glaucopsyche lygdamus palosverdesensis Perkins and Emmel." Occasional Paper of the IUCN Species Survival Commission. No. 8.

Perkins, E. M., and J. F. Emmel. 1977. "A New Sub-species of Glaucopsyche lygdamus from California." Proceedings of the Entomological Society, Washington 79:408-471.

U.S. Fish and Wildlife Service. 1984. "The Palos Verdes Blue Butterfly Recovery Plan." U.S. Fish and Wildlife Service, Portland.

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Palos Verdes Blue Butterfly

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