XERCES BLUE (Glaucopsyche xerces), first butterfly in the continental United States to have become extinct as a result of human activity. It was native to the coastal sand dunes of the San Francisco Peninsula.
Though tiny—its wingspan was barely an inch—the Xerces blue was renowned for its breathtaking beauty, its wings a mesmerizing iridescent blue that varied in intensity depending on the angle of light.
Because its habitat was restricted to the San Francisco Peninsula, and because it relied on only a few plant species (such as lupine) for both nectar and as a host for its larvae, the Xerces blue was especially vulnerable to human encroachment. Less than a century after the butterfly was first documented in 1852, it is believed to have gone extinct in the 1940s, a span of time during which San Francisco underwent rapid urbanization.
In 2021 researchers analyzed DNA from a ninety-three-year-old preserved specimen and established that Xerces blue had in fact been a separate species of butterfly and not an insulated population of a larger species.
The Xerces Society for Invertebrate Conservation, an international nonprofit dedicated to the protection of the natural world, is named after the Xerces blue butterfly.