Climate change stands out as the greatest current threat to biodiversity. But when discussing nature, it’s axiomatic that no matter how dire a threat, some species manage to benefit from the changing conditions.
A recent spate of Vineyard sightings of a formerly rare butterfly illustrates this counterintuitive twist. Already this August, the Island has produced 16 reports of red-banded hairstreak, Calycopis cecrops. For a species unrecorded on the Vineyard until 2016 and absent from all of Massachusetts until just a few years prior to that, it’s a remarkable count. But when you learn the full history of this butterfly, its sudden abundance here seems foreordained rather than surprising.
The species is a beautiful and distinctive one, basically gray but with a bold red stripe across the wings and a bluish eyespot at the outermost angle of its hind wing. This butterfly is about the size of a nickel when perched with its wings held up over its back — its typical posture. With wear, those colors fade; but on a fresh individual, that red stripe really pops, making this one of the most easily recognized of our 14 or so hairstreak species.
Turn-of-the-century observers (the turn into the 20th century, I mean) considered the red-banded hairstreak to be primarily a species of the Southeastern U.S. Vagrant individuals may have occurred farther north, but there is no evidence that the species ever made it to New England in those days. By midcentury, the species was at least occasionally north into New Jersey, and by the 1970s, it had crept northward to incorporate portions of Long Island, N.Y., into its range. (I’m grateful to historical research summarized on Sharon Stichter’s butterfliesofmassachusetts.net website for this account.)
But as the 20th century wound to a close, red-banded hairstreaks began turning up, initially as late-season vagrants, in southernmost New England. Twenty years later, there was no question that at least a few individuals were successfully overwintering in southern New England, and either vagrants or locally bred individuals were becoming routine. The inevitable first Bay State record came in 2011, from Longmeadow, and over the next few years, the number of Massachusetts sightings steadily increased, especially in the warmest portions of the state.
Red-banded hairstreak were first detected on Martha’s Vineyard in early September 2016, when a worn individual (very likely an immigrant) was photographed in a “pollinator patch” at Morning Glory Farm. A few days later, a second individual, this one fresh and possibly of local origin, turned up at the Nature Conservancy’s Woods Preserve in West Tisbury.
Four years passed with no further local records. But in August 2021, the species was photographed again at the BiodiversityWorks office off Lambert’s Cove Road. The next year brought three records, all in the same general area as the 2021 sighting. Fourteen records in 2023 suggested expansion of a breeding population through the northern portion of Martha’s Vineyard. And the records I know of from the current season show both consolidation within a core range in Tisbury and West Tisbury and expansion toward the south shore.
With winter conditions apparently now averaging mild enough so this species can survive reliably on the Vineyard, there is every reason to expect that red-banded hairstreaks will continue to build rapidly in abundance, and quickly colonize the entire Island. The plants that the larvae of this butterfly are common ones here (winged sumac and bayberry), so there is virtually no limit to the amount of suitable habitat the Vineyard offers.
In contrast to most butterflies, the larvae of which feed on living leaves, red-banded hairstreak is thought to be a detritivore — its caterpillars feed on the decaying leaves of its host plants. Apparently this butterfly can overwinter either in a late larval stage or as a pupa.
The year’s first generation matures from overwintering forms in May. A relative scarcity of Vineyard records from spring flights may suggest that the species still experiences considerable mortality during the winter. But even a few adults of that first generation now seem able to produce a significant second generation, with most observations of this flight coming in August.
Under suitable conditions, this species can produce three or more generations per year. (A mid-October record of a fresh individual in 2022 may be evidence that a partial third flight occurred that year.) Each generation represents another chance for the species to find and become established in new patches of habitat. A harsh winter may set this species back, but I’d be very surprised to see it even temporarily extirpated from Martha’s Vineyard; this elegant butterfly is now a permanent part of our fauna.
This story does not imply that I’m a fan of climate change. But in the case of this one butterfly species, novel conditions have worked out well. Red-banded hairstreak has vastly extended its range in the north, while giving up little if any ground in its ancestral southern homeland. And Martha’s Vineyard has a nice new resident.
