A perfect day for bug-hunting

Hundreds of flies, and some butterflies named for punctuation.

Tachinid fly in the genus Gonia. Photo by Matt Pelikan

My columns typically focus on one particular species that I’ve been able to learn something about. But sometimes my time in the field gets so fascinating that I gush about the overall experience.

Last Sunday was one of those days! It didn’t seem particularly auspicious for bug hunting: The season is still very young, with most vegetation still dormant and only a couple of plant species in bloom. And while the sun was bright, a chilly north wind kept temperatures in the low 50s. But my two-hour loop through the western half of Correllus State Forest turned up a little of everything.

The bug of the day was surely a fly in the genus Gonia, which was everywhere — I saw many hundreds. (The species in this genus are effectively indistinguishable in the field, so the genus name is the best I can do for an ID.) A bit larger than your typical house fly, mostly black with an improbable fuzzy nose cone, Gonia is in the family Tachinidae; their larvae parasitize caterpillars. They’re fast flyers and generally hug the ground, meaning the casual observer might easily overlook them. But they clearly had no problem finding each other: Courting pairs were all over the sand, advertising their availability with slow-motion wing beats.

Gonia outnumbered, but not by much, two other fly species: the fuzzy yellowish bee fly Bombylius major, equipped with distinctive two-tone wings and a straw-like proboscis (for sipping flower nectar) protruding in front of the face, and another spiny tachinid, Epalpus signifer. I saw hundreds of the bee fly and scores of this tachinid. This is not even to consider the other flies on the wing. Some I could identify; others were too small or too elusive for me to get good looks or photos, but all in all, I found at least 20 distinct types of fly.

These flies were pretty much expected, albeit more plentiful and diverse than usual. But coming as a complete surprise were some certifiable aquatic insects, out of place in the generally arid habitat of the Correllus State Forest sandplain. On one of the east-west fire lanes, a few deep wheel ruts were still full of puddled rainwater … and on these small puddles, I found water striders, a bug I’ve always considered restricted to permanent bodies of water.

Predatory insects able to “skate” on the surface tension of water, water striders (there are multiple species, and I haven’t yet worked on ID’ing the ones I found) are very common insects on Island ponds and streams. But it turns out the little devils can fly, and in fact, dispersing on the wing is a routine response for them when their population density gets high. The ones I found, at least a mile from any permanent surface water, had evidently gone walkabout and stopped on the puddles for rest and, perhaps, a chance to dine on a smaller insect.

Then there was the rarity. While it’s a common butterfly season-long in the rest of New England, the Eastern Comma is an enigmatic rarity on the Vineyard. There are a few firm records from the 1930s; since then, there have been a few sighting reports of varying degrees of plausibility, but no truly solid Island record for the species. In almost 19 years of butterfly-watching here, I’ve never seen one. The situation is clouded by the fact that the question mark, a closely related and quite similar butterfly, occurs regularly here, sometimes in respectable numbers, making misidentification a real concern.

So when I spotted a midsize orange butterfly trying to work north along a fire lane into the stiff wind, I assumed it was a question mark. I snapped a few bad photos, paying more attention to the viewfinder than the insect, since the date was a rather early one for a question mark. But when I reviewed the photos later on, boom! Eastern Comma! While some sight records in recent decades may well have been correct, this was probably the first documented occurrence of this species on the Vineyard in about 80 years. It was presumably a vagrant from a mainland population, blown here by the strong northerly winds.

And finally, there was beauty. Brown and Hoary Elfins, two of my favorite butterfly species, had begun flying. These tiny brown butterflies are an early-season specialty, on the wing for part of April and early May, and generally restricted to barrens habitats of the sandplain. I love their understated elegance.

There was more, but I’m running out of room! I think back 15 years when my insect interests were largely confined to butterflies and dragonflies. Back then I would have considered this a dullish early-season day, with just 13 individual butterflies representing six species and no dragonflies at all. But the diversity of nature is limited only by your knowledge and interest; the more you learn, the better it gets.