The Western Tailed-blue (Cupido amyntula) is a failry common resident of the Western States. The Eastern Tailed-Blue (Cupido comyntas) is one of the most widespreak blue butterflies in the United States. Abundant throughout the East, a small population also lives in California, Oregon and Washington State.
Identifying a Tailed-blue butterfly is fairly easy. Both species share the characteristic of small tails (hair-like protrusions) on the bottom of their wings, a physical trail they share with the hairstreaks.
Because both species look very similar, differentiating between the Eastern and Western species in the West is problematic at best.
The top picture shows a pair of tailed-blue butterflies with the characteristic double orange markings on the bottom of the wing edges.
Typically Western Tailed-blues are characterized by a single orange marking, however, the BugGuide images of Cupidos clearly shows both species having double orange marks on the underside of the wings.
Males of both species have a blue color on the top of the wings and females of both species have a darker brown or gray color on the top of the wings. The absence of orange border spots on the wings of the male in the second picture suggests it is a Western Tailed-blue.
The third picture shows a female tailed-blue with no suggestion on whether it is the East or West Coast species.
