All butterflies are beautiful. But in my view, one particular group, the hairstreaks, are the prettiest of the bunch. Small (about the size of a penny with their wings folded) and subdued in overall coloration, they’re nonetheless marked with intricate patterns of stripes and spots. They’re the gemstones of the Lepidoptera world.
At least when in fresh condition, most hairstreaks sport thin but readily visible “tails” — threadlike appendages on the trailing edge of the wings. Resembling antennae, these tails are thought to confuse would-be predators about which end of the butterfly is the front. It would take a deft predator to get close to a hairstreak, though; these butterflies are wary and launch into rapid, erratic flight at the least sign of danger. Photographing them, or even getting a decent look, can be a challenge.
Most of our hairstreaks (nine species) fly during the summer, mainly from late June into early August. A few have longer seasons, and one species in particular, the gray hairstreak, has one of the longest seasons of any butterfly on the Vineyard. The first ones usually turn up in the third or fourth week of April (April 14 is the earliest date I have a record of). And while abundance varies during the remainder of the season, gray hairstreaks can usually be found well into October. I even have a handful of early November Vineyard records.
This year, I ran into my first gray hairstreak on April 17, along a fire lane in the West Tisbury portion of Correllus State Forest. By the time this column appears, gray hairstreaks should be around their first peak of abundance; this will make them, if not exactly numerous, at least pretty easy for an informed observer to find. (On a good day, I find a dozen or more, and it’s a rare outing during the warmer months when I wholly miss this species.)
The early appearance of gray hairstreaks in the spring is easily explained. As warm weather winds down in the fall, larval gray hairstreaks finish their growth and pupate — that is, morph into the seemingly inert blob from which the adult butterfly will eventually emerge. Gray hairstreaks spend the winter in this pupal form, which means that when the weather begins to warm up in the spring, no further development is necessary: Adults are ready to emerge and start reproducing.
The species will run through several generations during the course of the season. Eggs laid by those individuals that overwintered will hatch, mature, and emerge as adults in late June or early July; the progeny of those will reach adulthood sometime in late summer; and at least a few of the offspring of that cohort will mature in late October, while the rest will cease developing at the pupal stage and prepare to overwinter. But these generations tend to be poorly synchronized; each generation produces a noticeable peak of abundance, but the process is untidy enough so that a few adults are almost always out there.
While some hairstreaks are incredibly finicky about habitat, the gray hairstreak is distinguished by being a generalist that seems able to reproduce almost anywhere. This trait makes it a very widespread butterfly on Martha’s Vineyard. Butterfly distribution is governed largely by larval host plant distribution: You tend to find a butterfly species near the type of plants that its caterpillars eat. And the gray hairstreak has among the broadest tastes of all butterflies.
Sources list more than 20 plant families eaten by larval gray hairstreaks, which probably translates to hundreds of plant species that this butterfly uses in one part of its range or another. In any given area, only a smallish subset of this vast range of host plants will be used. But still, this dietary flexibility makes it possible for gray hairstreaks to flourish nearly everywhere.
On the Vineyard, it’s clear that members of the legume family are the preferred host; I’ve seen gray hairstreaks laying eggs on a wide range of bush clovers, clovers, and trefoils. The best places to find this butterfly are where these species are common: Fire lane edges in the State Forest and the Old County Arboretum, a little triangular Land Bank property across the road from the West Tisbury School, are prime habitat.
But these hairstreaks clearly reproduce successfully in a wide range of Island settings, and they wander around enough so they can turn up nearly anywhere. They’re found reliably in my yard on the fringe of the Oak Bluffs metropolitan area, and I’ve found them “nectaring” on flowers in places as unnatural as Ocean Park in Oak Bluffs and along Main Street in Vineyard Haven.
Flat gray but exquisitely marked, the gray hairstreak is easily overlooked, but worth seeking out. And their unusual biology makes them by far the easiest of the hairstreaks to find. Look for them visiting flowers, sniffing around potential host plants, or perched on twigs, looking for a mate.