The easiest and most rewarding group of flies for amateurs like me to study is the family Syrphidae — that is, hoverflies or flower flies. True to the latter common name, adult flies in this family almost universally visit flowers for pollen and nectar, making them relatively easy to find. And by and large, flies in this family are boldly and brightly colored, making them both pleasing to the eye and easy to identify (at least to the genus, if not always to the species level).
But the process of evolution has been especially creative with syrphids, and indeed with flies generally. A lot of peculiar life histories and anatomy have arisen within this family, and I recently encountered an excellent example of just how weird things can get.
Hunting bugs in lovely, mild weather on May 3, I visited the Nature Conservancy’s Hoft Farm Preserve in West Tisbury. In short order I spotted a good-size fly, perhaps a centimeter long, perched on bare soil in a damp, shady spot. Making quick camera adjustments to accommodate the dim light, I closed in carefully for a good look and some photos.
Three features instantly struck me about this fly. First, it was mostly covered by short, dense, golden fur; even the eyes were visibly fuzzy. Second, the markings on the body were bold but muted. Third and most striking, this fly possessed long, flattened, swordlike antennae, an unusual feature among flies, and one that immediately pinned this individual as a member of one of a few rather small taxonomic groups.
The body hair, which softened the fly’s outline, and the muted markings fooled my camera’s autofocus. So I resorted to manual focus to snap most of the dozen or so frames I managed before the fly abruptly departed. Only four of the photos were any good, but because of the fly’s odd anatomy, those shots sufficed to make identification quite easy: this was the syrphid fly Callicera erratica, a new genus and species for me. It is also known by the common names American golden longhorn (after those wonderful antennae) and golden pine fly.
Researching this species revealed first its rarity, or at least the rarity with which humans find it. C. erratica is known from scattered records across the Eastern U.S., but it is a fly that even many fly specialists have never seen on the hoof. I’m quite sure there are no previous Martha’s Vineyard records, and I could find only one other record from all of Massachusetts: An individual snagged in Amherst in 1963 resides in the Smithsonian’s insect collection. A more recent record from near Hartford, Conn., represents the only other New England record I can track down.
But learning about this fly’s life history made me wonder whether it is truly rare, or just rarely observed. It apparently spends most of its time in the forest canopy, where adults, active in the early spring, feed on pollen or nectar on trees including willow, cherry, and red maple. Adults are known to visit damp ground occasionally, presumably to ingest minerals along with water, and this is no doubt what my fly was up to when I stumbled onto it.
Larvae of this species are also arboreal, and here it is where it gets strange. They live exclusively in small cavities in trees, such as you might find where a rotting branch connects to the trunk, and they feed primarily on bacteria associated with decaying wood. The larvae, one source reports, may take as long as five years to reach maturity. This is wildly atypical for a fly, given that this order in general specializes in rapid reproduction to take advantage of transient resources. And the mind boggles to think that some intrepid entomologist managed to figure all that out!
An informative species page on the New York Natural Heritage Program’s website (https://guides.nynhp.org/golden-pine-fly) adds information that makes my sighting seem atypical: “These arboreal, canopy-dwelling flies,” that website opines, “are confined to old-growth pine/oak forests with senescent trees, where the larvae live in rotholes and water-filled cavities of old living conifers.” But the woodland I found my fly in is far from old growth, and the immediate setting of my sighting included no pines at all.
The key thing from this fly’s perspective, however, may not be so much the age or species composition of the forest as it is the presence of suitable cavities for larval development. And the notorious dampness and humidity of Martha’s Vineyard may promote rot even in young trees, offering the larvae of this fly hospitality in forest types that the species would normally be unable to occupy.
When biologists talk about the distinctive biodiversity of Martha’s Vineyard, this is precisely the kind of thing they mean. Callicera erratica, rare or at least rarely observed, just turned up here handily outside the previously known range for the species. And it’s living in woodland significantly different from what the species is thought to prefer, or indeed require. With insects as with people, the Vineyard hosts unique populations.
