The specific name derives from the French spelling of "Xerxes", the Greek name of the Persian kings Xerxes I and Xerxes II of the fifth century BC.[5] An endangered invertebrate conservation group known as the Xerces Society is named after the Xerces blue.[6][7]
The species was first described and documented in 1852.[9] It was characterized by blue wings with white spots.[10] The butterflies fed on vegetation belonging to the genus Lotus and Lupinus.[10] The loss of the Lotus plant that the butterfly fed on while in its larval stages is believed to be one reason for the extinction of the Xerces blue. The plant could not survive in the disturbed soils due to human development, and was no longer available to the Xerces blue.[9][10]Lupinus, the Xerces blue's other vegetative food source, was not suitable for the larval stages.[10]
Efforts are on to reestablish related butterflies in the Xerces blue's former habitat. The Palos Verdes blue (Glaucopsyche lygdamus palosverdesensis), which is considered a Los Angeles cousin of the Xerces, is being reared in labs.[citation needed] A new Xerces-like subspecies of the silvery blue (Glaucopsyche lygdamus), which the Xerces blue was thought to be a subspecies of[11] has been discovered as well, and is being analyzed as a potential way to revive the Xerces blue.[12]
