Our   species profile for this issue is the Western Tailed Blue, Everes amyntula.  The Western Tailed Blue belongs to the family Lycaenidae, the large worldwide family of butterflies which includes all blues, coppers, hairstreaks and metalmarks.  

Lycaenids are typically small, nectar-feeding species, prone to mudding on sunny days. In the portion of the group which we call “blues” the dorsal wing coloration is typically blue in males and brown in females, while both sexes have a whitish to grey ground color ventrally, punctuated with dark spots or lines and sometimes orange spots or bands. In Washington there are 42 species of Lycaenids, 16 of which are blues.

The Western Tailed Blue is a common species in Washington, especially in meadows and along roads or other clearings in forested areas. Look for this pretty blue butterfly when the spring wildflowers are in fresh bloom, but remember that the tails are easily broken and often missing. Watch for this species in mixed aggregations of blues at mudding areas, or seeking nectar at flowers.

The Western Tailed Blue occurs throughout much of Alaska, and south through western Canada and the western USA, extending slightly into Mexico. The species does not extend very far east of the Rocky Mountains in the US, but in Canada its range sweeps much further east to the Great Lakes.

The Western Tailed Blue first emerges in Washington in late March or early April and can be found through mid-July at higher elevations. The species is regarded as single-brooded this far north, but outlier sightings into late September strongly suggest that a small portion of the population may be double-brooded. The species overwinters as a mature larva or chrysalis, although reports in the literature are somewhat contradictory.

The eggs are small, white or light green, of typical Lycaenid shape (like a squished tennis ball), and are laid singly at the base of flowers where pea pods will soon grow. In this area the favored food plants are Vicia (vetch) and Lathyms (wild sweet pea). When the larvae hatch they bore into the pea pods, eating both the pod and the internal peas. Contrary to reports in the literature, they do not always seal their entry holes, and in fact may sometimes be found feeding on the exterior of the pea pod.

The larvae are pale green with short white hairs and a two-tone white and brown ventrolateral line.  At maturity the larva turns brown and enters diapause, its hibernation stage. It is unclear whether the larva always pupates the following spring, or if it sometimes does so in the fall, but it is likely that both strategies are used on occasion.

The eggs of the Western Tailed Blue can be found by carefully examining the base of Lathyrus blossoms and nearby plant stems while the plant is in full bloom. Later the larvae can be found on the same plants by examining the pea pods for small round entry holes. Other insects also bore into such pods as well, although a single plant is seldom host to more than one species.

The Western Tailed Blue, and its sibling species the Eastern Tailed Blue, are the only blues with tails in Washington. Some hairstreaks may be dark blue dorsally and have tails, but they do not rest with their wings open as the Blues often do.

In Washington the Western Tailed Blue is very pale ventrally, sometimes almost pure white, with a few distinct small black spots and a distinct orange “thecla spot” near the tail. In other regions the species may be darker on the ventral side. The males are bright blue dorsally with a white fringe, and females are brown with a distinct reflective blue cast and a row of black-on-white marginal spots along the dorsal hindwing margin.

The Eastern Tailed Blue is very similar but is darker ventrally, with more pronounced black spots, and is confined to the far eastern and northeastern parts of Washington.

Note: All photos are by David Nunnallee.

G’num2002Vol3No3