The Palos Verdes blue butterfly (Glaucopsyche lygdamus paloverdesensis), a subspecies of the silvery blue, was discovered in the early 1970s . It was originally found on the cool, fog-shrouded seaward side of the Palos Verdes Hills on the Palos Verdes Peninsula in Los Angeles County  and was subsequently found on the inland side of the peninsula . The Palos Verdes blue (PVB) is dependent on two known host plants, locoweed (Astragalus trichopodus var. lonchus), also known as Santa Barbara milkvetch, and common deerweed (Lotus scoparius) . An adult flight period occurs from late January through mid-April . Eggs are typically laid in the flower heads of either deerweed or locoweed, where the caterpillars then feed . When the larvae mature, they crawl into the leaf litter to pupate. The pupae emerge as the next generation of adult butterflies in spring .
The historic PVB population was likely continuous across the 5000 ha of coastal scrub habitat that covered the south half of the Palos Verdes peninsula . Intensive development of this area began in the 1950s and by the time of its discovery in the early 1970s, the PVB was already reduced to a few habitat fragments. By 1994 the 500 ha of habitat remaining was not continuous and consisted of a mosaic of coastal sage scrub assemblages interspersed with disturbed patches . When the Palos Verdes blue was listed in 1980, three localities known to support the species were listed as critical habitat . Host plants on two of these sites were extirpated by 1985 due to the spread of weeds and annual grasses . At the third site, construction by the city of Rancho Palos Verdes at Hesse Park in 1982 (in violation of the federal Endangered Species Act) destroyed what was then probably the second largest remaining PVB colony . This resulted in a lawsuit against the city. Legal action was dismissed, however, under the theory that a city could not be held liable .
Although population numbers were not estimated in the 1980s, there were probably fewer than 300 adults among all remaining habitat fragments . In 1983 there were sightings of only 4 to 7 adult PVBs . Loss of habitat in combination with extremely harsh winters in 1983 and 1984 was thought to have led to the extinction of the PVB . For 11 years, the PVB was thought to be extinct. Then, in 1994 the butterfly was re-discovered at the Defense Fuel Support Point managed by the Department of Defense at San Pedro, California .
The rediscovered population was composed of only a few hundred individuals . Because this single population was in danger of extinction from stochastic factors, a captive propagation effort was started and efforts to restore habitat were initiated . The captive rearing program has maintained a captive population of PVB since 1995 . Breeding results were poor from 1995 to 1998 but saw increased success in 1999 when 627 pupae were produced. In 2000, 968 pupae were produced . In 2004, 231 were produced [followed by 93 in 2005 . Since 1994, captive reared butterflies have been used to augment the existing colony and in 2000 pupae were reintroduced to a nearby natural area, known as the Chandler preserve, which resulted in the emergence of 306 PVB adults . The reintroduced butterflies mated and eggs were deposited on over 1,000 food plants on the 6-acre natural area . It has yet to be determined whether this introduced population has persisted . By 2000, 17 acres around the Defense Fuel Support Site had been planted with native vegetation .
Estimated PVB populations have fluctuated without a discernible trend since 1994 . In 2003 the population dropped from an estimated 215 individuals to 30 but recovered to 282 in 2004  and 204 in 2005 . Large increases and decreases in population are expected since butterfly abundance is known to vary with environmental conditions, especially with weather, and because they may be capable of multi-year diapause . Because this makes the detection of trends difficult, the number of locations that support the butterfly is likely more important than the total number of butterflies at those locations . An analysis of occupancy trends at monitoring transects suggests a decline in area occupied by the PVB . Although this could be due to actual declines, it could also indicate a shift in occupancy . Monitoring transects have remained at fixed locations, and it is possible that the butterflies have moved as successional habitat matured . Regardless, recovery efforts should concentrate on providing more habitat for the PVB. Currently weed control efforts, off-road vehicle use, non-native plant invasion, and fire suppression negatively impact PVB habitat .
 Mattoni, R. 1995. Rediscovery of the endangered Palos Verdes blue butterfly, Glaucopsyche lygdamus palosverdesensis Perkins and Emmel (Lycaenidae). Journal of Research on the Lepidoptera 31(3-4)180-194.
 The Butterfly Conservation Initiative. American Zoo and Aquarium Association. The Palos Verdes Blue Butterfly. Website http://www.butterflyrecovery.org/species_profiles/palos_verdes_blue/
 Longcore, T. 2005. Personal communication with Travis Longcore, Urban Wildlands Center, University of California.
 Arnold, R. A., 1987. Decline of the endangered Palos Verdes Blue Butterfly in California. Biological Conservation 40(3):203-217.
 Mattoni, R., T Loncore, Z. Krenova, A. Lipman. 2003. Mass rearing of the endangered Palos Verdes blue butterfly Glaucopsyche lygdamus palosverdesensis (Lycaenidae). Journal of Research on the Lepidoptera. 37:55-67.
 Mattoni, R. and N. Powers. 2000. The Palos Verdes Blue; an Update. The Endangered Species Bulletin. 25(6).
 Longcore, T., and R. Mattoni. 2005. Final Report for 2005 Palos Verdes Blue Butterfly Adult Surveys on Defense Fuel Support Point, San Pedro, California. Los Angeles: The Urban Wildlands Group (Defense Logistics Agency Agreement # N68711-05-LT-A0012). 11 pp.