The Palos Verdes blue (Glaucopsyche lygdamus palosverdesensis) is a small endangered butterfly native to the Palos Verdes Peninsula in southwest Los Angeles County, California, United States. As its distribution has been proven to be limited to one single site, it has one of the best claims to being the world's rarest butterfly.

Overview

The Palos Verdes blue (G. l. palosverdesensis) is a localized subspecies of the silvery blue (G. lygdamus), which ranges over much of North America. It was described in 1977, shortly before it became one of the second groups of butterflies to be listed under the US Endangered Species Act in 1980. It is distinguished from other subspecies of G. lygdamus by its slightly different patterning on the underside of the wing and an earlier flight period. The subspecies was described from the southern slope of the Palos Verdes Peninsula in coastal Los Angeles County.

The Palos Verdes blue butterfly was thought to be driven to extinction in 1983, primarily by development of its habitat.

Morphology

The Palos Verdes blue butterfly has a wingspan of only . The male has a bright silvery-blue dorsal wing outlined in a narrow line of black, while the female's dorsal wing is a more brownish-gray colour. Both males and females have gray ventral wings with dark spots surrounded by white rings.

Habitat

G. lygdamus palosverdesensis persists particularly on the Palos Verdes Peninsula, 15 miles south of Los Angeles, in a coastal sage scrub habitat. This subspecies is locally monophagous, or particular to one species of food plant. The entire subspecies was originally thought to be particular only to the locoweed or rattlepod (Astragalus trichopodus lonchus), but the population rediscovered in 1994 used common deerweed (Lotus scoparius) as its larval food plant.

Relationships with other species

Interspecific competition may occur with other lycaenid butterflies for the larval food plant. A mutualism between ants and larvae has been observed during the instars of butterfly development. G. l. palosverdesensis has a host-parasite relationship with its larval food plants, Astragalus lonchus and Lotus scoparius. Predation by western yellowjackets (Vespula pensylvanica) on the Palos Verdes blue has also been observed at the Defense Fuel Point location.

Court case

In 1982, the city of Rancho Palos Verdes bulldozed the then most extensive known habitat of the butterfly to build a baseball field, an act believed to have been a principal cause of the die-off of the subspecies before its rediscovery in 1994. The US Fish and Wildlife Service maintained that the city was "well aware" of the butterfly and the site status. According to the Los Angeles Times, the mayor of the city "said no one complained about butterfly destruction until grading had been completed." and thus could not be held criminally responsible.

Since that time, the Defense Logistics Agency, which operates the facility, has funded habitat restoration and a breeding program for the blue butterfly. Honey, produced on the premises, is provided to the captive rearing program so the butterflies are able to feed on the same food source as its wild companions. Major Jason Pike, an entomologist for the Defense Logistics Agency who has been monitoring the project, commented, "The military takes its responsibilities for endangered species on its properties very seriously, and DLA is pleased to provide support for the blue butterfly project."

Mass rearing

Mass rearing of the Palos Verdes blue has been taking place since rediscovery in 1994. The mass rearing is conducted for conservation purposes, reintroduction and prevention of extinction. The mass rearing takes place in "tent" cages containing both known larval food plants. It has been variably successful. In 2008, 2,400 butterflies were raised in a laboratory at Moorpark College. In addition to accepting the conditions of the butterflies' protected status, landowners seeking to house the butterflies needed to prove they could provide sufficient numbers of "yellow-flowering deer weed plants."

Modeling

Although population viability analysis models are often very important for predicting the outcome of conservation efforts, there have been many problems with using population viability analysis models to predict Palos Verdes blue populations. This type of modeling has proved inconclusive mainly because the Palos Verdes blue utilizes habitat so variably, depending on climatic and successional changes.

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