Entry 37: The Xerces Blue (Glaucopsyche xerces)

Once a gossamer-winged butterfly of the Lycaenidae family, fluttering about the sand dunes of San Francisco’s Sunset District, the Xerces Blues was first described in 1952. They possessed a purplish-blue wing with light white spots. Their unique symbiotic relationship with ants when in the larval stage was probably part of the reason for their downfall.

With westward expansion brought urban development as well as the introduction of a non-native ant species that likely disrupted the dependence on the local variety. Last seen in the Golden Gate National Recreation Area, they are thought to be the first American butterfly species to go extinct as a direct result of urban development.

Extinction Date According to the IUCN Red List: 1941