Wild Side: Insects are still out there

A resourceful biologist stumbles on a fascinating ‘storm door find.’

A small wasp of the Brachymeria genus rests inside the storm door. — Matt Pelikan

As November winds down, bugwatching likewise grows slow. All of the Island, by this point, has had at least one hard frost, killing many invertebrates. And even without a frost, many insects have simply run their course by late November, senescing and dying, their roles as procreators, predators, and prey concluded.

But I’m a resourceful guy. Over the years, I’ve figured out many tricks for finding bugs in late fall and winter. Some species routinely overwinter as adults; individuals of other species may simply survive a bit longer than their conspecifics. So if you know where to look, insects are still out there.

One key location is the pocket of warm air between our front door and its storm door. Facing west, the front door warms up in the afternoon sun, and on all but the coldest or cloudiest days, the result is a microclimate that nearly any insect would be happy with.

How they find this location, and how they get in, are questions I can’t completely answer. Perhaps the configuration of the panes in the storm door works as an ad hoc insect trap, with bugs that have an instinctive urge to go upward when they hit an obstacle — working up the lower pane and entering through the gap where the panes overlap. Or perhaps crevices leaking warm air invite entry (it doesn’t take much of a gap to allow an insect through).

In any event, while the front door trick doesn’t work every day, it produces bugs pretty regularly through the winter, and sometimes the species involved are interesting ones.

On Thanksgiving Day, I kept an eye on the door, figuring that the weather was warm enough to prompt some insect activity. A few blowflies showed up — these regularly overwinter as adults — and a couple of lady beetles, seeking a mild spot to overwinter. But it was a tiny black-and-yellow insect that caught my eye.

Perhaps four millimeters long, this critter was stoutly built and featured thick antennae and bulbous femora, or thighs, on its hind legs. I nudged it onto a fingertip, hoping to move it into better light so I could photograph it, but just before I tripped the shutter, it took flight.

Responding like any self-respecting naturalist would, I cursed violently, then began searching the living room for my quarry. Amazingly, I found it, just a few minutes later, parked in the same patch of sunlight I had been trying to move it to!

Once I had some photos to work with, the process of identifying it went quite smoothly. It’s not always the case, but odd-looking insects (and this one was odd-looking in spades) are usually easier to ID than generic-looking ones. In this case, the long, stout antennae ruled out a fly of any kind, and the overall structure strongly suggested a wasp.

Many small wasps, and in particular ones with oversize femora, fall into a wasp division called “Parasitica.” It’s a catch-all designation, incorporating many evolutionary lineages that happen to share parasitic life histories. With Parasitica as my initial guess, I began scanning the 11 superfamilies in Parasitica on the website bugguide.net.

That site, a vast archive of identified arthropod photographs organized by taxonomy, offers a handful of representative photographs for each group. Using Bugguide, you simply narrow things down as far as you can from your existing knowledge, then scroll through offerings at that taxonomic level, looking for and clicking on groups that have photos matching what you’re trying to identify.

In this case, from “Parasitica” I quickly zeroed in on the superfamily Chalcidoidea, and then, perusing the options there, tried the family Chalcididae. Among the Chalcidids, the genus Brachymeria stuck out as a very close match for my mystery wasp.

Brachymeria is a large genus, but poorly studied, with more than 300 species worldwide and somewhere around 30 species in North America. But only a minority of these species seem to be represented by photos on the internet, and reliable information on how to identify these wasps is scarce. So genus is probably as far as I can get.

Belonging to Parasitica, the members of Brachymeria all have parasitic larvae. From eggs laid on or near a suitable host, Brachymeria larvae burrow into their victims and eat them from the inside out. For most species in the genus, Bug Guide reports, the hosts are moths, with the wasps probably parasitizing moth larvae, or caterpillars, rather than adults. Brachymeria is evidently good at the game: Bug Guide notes that some species are used as biocontrol agents for pest moths.

This was my first experience with this interesting genus. I can’t find any previous records for the genus from Martha’s Vineyard, though it may be common here, just overlooked. In any case, it was a good “storm door find,” and a welcome diversion at a dull point in the bugwatcher’s year.