Our species profile for this issue is the Johnson’s Hairstreak, Mitoura johnsoni.

Hairstreaks belong to the large worldwide family Lycaenidae, which also includes all blues, coppers and metalmarks. Hairstreaks are generally small butterflies, often with taillike extensions, or “hairstreaks”, on their hindwings. In Washington State there are eighteen species of hairstreaks, three of them in the genus Mitoura. All Mitoura are generally rather scarce and highly sought by butterfly enthusiasts. All three species have a close association with evergreen trees, the larvae of one feeding on cedars or junipers (Cedar/Juniper Hairstreak), and the other two feeding on dwarf mistletoe growing on evergreens (Thicket and Johnson’s Hairstreaks). All three Mitoura species have distinct white lines on their ventral hindwings, contrasting with a darker ground color of various brown or purplish tones.

This species is found only near stands of old growth Hemlock trees which are host to dwarf mistletoe. In these scarce areas of suitable habitat adult johnsoni sometimes venture to the ground to nectar where they may be found on any nectar-producing flowers which may be in season, or on damp ground or basking on rocks. Where they fly with their close relatives the Cedar Hairstreaks, johnsoni seem to nectar less and bask more than their cousins. When disturbed johnsoni tends to fly up into the trees.

The Johnson’s Hairstreak life cycle is inextricably entwined with that of a species of dwarf mistletoe, Arceuthobium tsugensis, which grows as a parasite on Hemlock trees, and johnsoni apparently requires infested old growth Hemlock.

As its host plant dies back each year, Johnson’s Hairstreak flies in mid spring, usually around Memorial Day at lower elevations, after the Arceuthobium has begun to sprout new growth. Adult butterflies usually come to the ground only to nectar, spending most of the time high in the canopy near their food plant. Adults are most easily seen on steep slopes, where the ground level is near the canopy-level of nearby trees. Eggs are laid singly on the dwarf mistletoe, often tucked deep into the many crevices of the plant. On hatching the tiny yellow-orange larvae blend extremely well with the similarly-colored host plant. The larvae cling tenaciously to the host plant; in nature a slip would probably be fatal.

On growing larger the larvae become beautifully patterned, albeit still in extremely well-camouflaged yellows and greens. The larvae eat the Arceuthobium buds using their extendable necks to hollow out the buds, producing a recognizable feeding pattern. On maturity the larvae move to an area of dense needles in or adjacent to the Arceuthobium where they pupate, still high in the trees, anchoring themselves only with a single thin silk girdle thread. There they diapause until the next spring when they will emerge and fly again. In Washington there may be a partial second brood, and further south the second brood is probably more pronounced. The Johnson’s Hairstreak, with its distinct jagged white ventral hindwing line contrasting with a dark brown ground color, can be confused only other species of Mitoura. Its western Washington range mostly overlaps only with that of Mitoura grynea, the Cedar (Juniper) Hairstreak, from which it is distinguished by Johnson’s larger size, less jagged white line, and the absence of any purplish color on the ventral hindwing. In the very few areas where johnsini might overlap with the Thicket Hairstreak, such as Skamania County or eastern King County, spinetorum will be seen to have a more reddish chestnut-brown ventral hindwing compared to the subdued dark brown of johnsoni. Also spinetorum has dark submarginal spots around the entire periphery ofthe ventral hindwing, while on johnsoni the spots are only on the rear half of the wing. Dorsally johnsoni is brown, spinetorum is blue.

Mitoura johnsoni is under consideration for listing under the state endangered species act.

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