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Beetles

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While there are plenty of dull-looking examples, beetles as a group include a lot of striking insects.

Even with frosty nights still lingering, ground beetles like this gnarly black Meloe are out and about, doing their thing. — Photo by Matt Peilkan

The earliest days that feel like spring rather than late winter are among my favorite days of the year — after the last of the snow has melted, and plants are just starting to break out of dormancy. It’s a time when the world still looks dead and it’s hard to imagine any insects stirring, until you look more closely and see that, in fact, a surprising variety of hardy bugs are on the move.

Following a crummy winter, it was not until this past weekend that it felt like spring had taken charge on the Vineyard. Sunday was not quite as warm as the bright sun suggested — our thermometer read 42 around noon. But the ground was thawing, and I inevitably ended up in Correllus State Forest, where sun-warmed soil along the fire lanes yields interesting early-season arthropods, as early as mid-March in some years.

It takes a certain amount of audacity for a cold-blooded insect to be out and about at this point in the season. A week ago, there was snow on the ground, and temperature at night still drops regularly below freezing. But the sun, shining stronger and longer with every day, can easily heat an insect up to operating temperature. For the relatively few insects that have mastered the problem of freezing while they’re in an active state, early spring is perfectly workable.

While there are plenty of dull-looking examples, beetles as a group include a lot of striking insects. An excellent example would be the so-called “oil beetle” I ran into on Sunday. More formally it’s a species (I can’t tell which one) in the genus Meloe. The six or eight species that seem possible on the Vineyard differ only in very subtle ways, but the odd qualities they share go well beyond the bloated, almost wingless, glossy black form these inch-long beetles take as adults. I find what I assume is the same species more springs than not on the same stretch of fire lane, and it makes me happy that I know a place where I can reliably find such a creature.

The name “oil beetle” (or “blister beetle,” a more general name for the entire family) derives from a bizarre defensive trait these insects have evolved. By and large, they’re sluggish insects, and you can tell by its looks that they are flightless and about as agile as a washing machine. But don’t mess with them. When disturbed, they’re said to exude a caustic chemical from their joints, a juice gnarly enough to raise blisters. This is not something I’ve felt it necessary to confirm by personal experience!

The life cycle of Meloe is bizarre as well, at least to human sensibilities, though it’s actually pretty tame by insect standards. Like most blister beetles, the members of this genus are known to be parasites of ground-nesting, solitary bees. Living as individuals rather than in colonies, such bees lay their eggs in burrows they’ve provisioned with pollen or other food for their offspring to eat while developing. In effect, a bee nest is a little cache of resources, and blister beetles, like a surprising number of other insects, have found a way to purloin it.

Blister beetles exploit the frugal provisioning habits of the bee by laying their eggs on flowers that the bees are likely to shop at. The larval beetle — which are even homelier than the adults if that’s possible — simply latch onto a bee’s body hair and hitch a ride to a burrow that’s being provisioned. There, the beetle grub lives on whatever the adult bee provides, and occasionally on the eggs or larvae she has produced.

At least some blister beetles reportedly locate areas rich in the appropriate kind of bee, whether by detecting the bees themselves or perhaps just by having an instinctive love of the same habitat the bees prefer. And while the associations of parasites and hosts is a vast subject that we know very little about, at least some blister beetle species are known to successfully parasitize only very specific bee species. Again, such tight and obligatory relationships aren’t unusual in the insect world.

Oddly, a second blister beetle species was on the move on Sunday, one that I had never encountered before. Tricrania sanguinipennis (it seems to have no common name) is smaller and has a more conventional shape than its cousin Meloe, with a prettier orange-and-black color scheme. But it shares much of the same biology. The females of both these species will mate and lay eggs in carefully selected sites as the spring progresses. The resulting larvae will waylay the requisite bees and, after maturing underground during the course of the summer, overwinter until the earliest spring days next year.

When I’ll be looking for them.