The olive hairstreak is Missouri’s only green butterfly. The underside has white and brown lines on both wings. The underside main color varies among individuals, some being greener and others more brown. Like nearly all other hairstreaks, the hindwings have tails. If you get the rare chance to see the upperside of the wings, you’ll see they are orange with brown borders. Springtime individuals are more orange above than those of the summer brood, which are darker brown above.
Larvae are green, with lines of small whitish slanted marks on the sides. Like other hairstreak caterpillars, they are short, chunky, and rather sluglike.
Habitat and Conservation
Locally abundant in association with red cedar in the Ozarks; less commonly encountered in other regions of the state.
Taxonomically, this species — called the juniper hairstreak, Callophrys gryneus — has been debated for a long time. Currently, it is viewed as a single, widespread species ranging over much of North America, but with more than a dozen subspecies. Many of them are in the western US, where various junipers and related conifers are abundant. Missouri’s subspecies, called the “olive hairstreak,” is subspecies gryneus. The different subspecies vary in different regions by coloration and patterning, and they have different regional species of cedars to eat. But they appear to interbreed freely with each other, so at this point they are considered just regional variations, and not different species.
Ecologists have figured out that eastern red cedar used to be pretty uncommon in Missouri. Today, this is hard to picture, because cedars, which readily colonize open ground, are now found nearly everywhere. But before European settlement, fires regularly swept through Missouri habitats, preventing cedars from getting established. Before settlement, prairies, savannas, and even Ozark woodlands and glades all lacked cedars. Where were the olive hairstreaks, then? Perhaps they, too, were uncommon in our state.
Before pioneer settlers arrived and started suppressing fires, the only places cedars could survive were on protected rocky bluffs and cliff faces — places where fire couldn’t reach them. With fires eliminated, cedar populations expanded tremendously. With olive hairstreaks so connected to cedar trees, do you suppose they, too, have increased their populations since the arrival of Europeans?
Camouflage can be critical for a butterfly’s survival, helping it avoid predators. The spring and summer colors of olive hairstreaks are probably subtle changes that help them blend with the two different colors cedars go through each year — bronzy red in winter through early spring, when bright green needles appear, and then rich, dark green after the new needles reach full size.
"Plant-insect interactions" is a rich field of study. At least one biologist has theorized about the juniper hairstreak’s odd taste in food plants. Most other hairstreaks have dicots as their larval foods (dicots are non-conifer flowering plants, such as wild plums and cherries, oaks, hickories, sumacs, legumes, and mints) — but this species eats conifers: members of the cypress family, notably cedars (junipers). How did this come about? It turns out that some of this species’ closest relatives eat the foliage of mistletoes (which are dicots). And many mistletoes are parasitic on junipers. The ancestors of juniper hairstreaks might have shifted from mistletoes to junipers, which would provide them with a more stable food source, since mistletoes may easily die or be broken off of their host trees.