"Hairstreak" is an informal name for a group of generally similar butterflies in the family Lycaenidae. Most (not all) are basically gray butterflies; all have intricate patterns of markings on the undersides of their wings. (The underside is all that one normally sees of hairstreak wings; like most Lydaenids, they generally perch with their wings held together over their backs). Some hairstreaks have a long season on the Vineyard, with multiple flight periods; other species are limited to one flight period, generally in summer, from late June to early August. Look for hairstreaks either perched on leaves or the tips of twigs, or else nectaring on flowers such milkweed. Most hairstreaks have fine, threadlike "tails" projecting from the edge of their hindwings. For our early-season "hairstreaks," see the guide to Martha's Vineyard elfins.
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