The Arrowhead Blue is a member of the family Lycaenidae, the large worldwide family of butterflies which includes all blues, coppers and hairstreaks. In Washington there are 46 species of lycaenids, 20 of which are blues. Only two of Washington’s blues are in the genus Glaucopsyche, this species and the closely-related Silvery Blue, Glaucopsyche lygdamus.

The flight period for Glaucopsyche piasus in Washington is mid-April to early August. The Arrowhead Blue is a rather uncommon species in Washington but occurs over a large area east of the Cascade Mountains. Beyond Washington G. piasus occurs throughout much of the western US. The larvae of G. piasus feed on lupines and adults are seldom found far from these food plants. Lupinus sericeus (Silky Lupine), L. laxiflorus (Spurred Lupine) and L. wyethi (Wyeth’s Lupine) have been confirmed as host plants here. The preferred habitat includes areas where lupines flourish, from the shrub-steppe into montane areas, but the species is generally absent from heavily timbered regions.

Adults eclose in mid to late spring and soon begin courtship. After mating females oviposit on the tight, unopened flower heads of Lupinus, tucking eggs singly down between the buds or placing them on the sides of the unopened racemes. The larvae apparently always remain on the flowers of the host plant until pupation; hatched eggs found on blooming lupine flowers indicate that oviposition is timed to enable first instars to exploit new blossoms. Eggs can be obtained from captive females on a fresh host plant or can be found in the wild by searching unopened flower buds of the host plant in areas where G. piasus flies. However other lycaenids, especially Plebejus icarioides and Glaucopsyche lygdamus, may oviposit on the same plants and the eggs are difficult to separate. Development from L1 to pupa appears to be about 25 days and development from oviposition to pupa is probably about 30 days. On July 20 in Chelan County, three larval instars, L2-L4, were found on L sericeus at the same time suggesting that oviposition occurred over an extended period of time. Of fifteen larvae found, all were on the pods of Lupinus sericeus and all were tended by ants; in fact the larvae were most easily found by searching first for the tending ants. In all cases the larvae were on or immediately adjacent to L. sericeus pea pods, and many of the pods had neat round holes bored into them, the result of larval feeding. In several instances the larvae were found with their heads and necks extended into the pods.

There were no indications that the larvae fed on any part of the lupine other than the fruits although early hatchlings must feed on the flowers as the peas are not yet developed at that time. Wild collected larvae are easily reared by placing them with fresh pods from their host plant; there are reports that even grocery store fresh peas can be used. The larvae of G. piasus do not build nests at any stage, although the final instar places a thin mat of silk on the surface where the pupa will be attached. This species is single-brooded and the pupa is the overwintering (diapause) stage.

The Arrowhead Blue is arguably the most attractive and most easily identified of Washington’s blues. This species is larger than many of the other blues, and the white “arrowheads” on a gray or brown background on the ventral hindwing is a unique and diagnostic pattern. Adults appear larger and darker in flight than other blues which fly with them.

All photos this page by David Nunnallee

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