By Joe Rankin
A while back I had a few hives of honey bees parked at a beef farm down the road, tucked up against a stone wall just outside a pasture. One day the owner called to say that my bees had invaded a building in a barn complex and were laying eggs in manure puddles.
I went down to check it out, and the building did have a lot of buzzing insects butting their heads against the windows. I looked closer. They looked like honey bees, but . . . not quite. And there were weird larvae wriggling in the water seeping from manure.
I assured my neighbors that they weren’t going to get stung by those “bees,” then hot-footed it home to do some research. It didn’t take long to identify them as drone flies, Eristalis tenax, a member of the family Syrphidae, the hoverflies. According to the National Audubon Society’s “Field Guide to North American Insects and Spiders,” while adult drone flies feed on nectar and pollen, their larvae (called rat-tailed maggots for the snorkel-like breathing tube at the tip of the abdomen) are famous for being found on carrion and open latrines. In fact, this fly is likely the source of the myth that honey bees develop in dead animals, a story that goes back to the Old Testament.
The drone fly is a common bee mimic. But it’s not the only one. There are hundreds of species of hoverflies, and most of them mimic bees of one kind or another, says entomologist Jason Dombroskie, the manager of the Cornell University Insect Collection and coordinator of the Insect Diagnostic Lab.
“The mimicry can be quite impressive,” he noted. “If you look at popular media articles on anything to do with bees, there’s a good chance that that stock photo they choose will not be of a bee. There’s a good chance it will be a fly.”
Bee and wasp mimics are exhibiting Batesian mimicry, named after English naturalist Henry Walter Bates. They’ve evolved colors and behaviors that mimic those of insects with a reputation of stinging if messed with, but not the sting itself. Most commonly, they’ve evolved some variation of yellow and black banding that signals STINGING INSECT! “We associate yellow and black with danger, even though most bees are not aggressive,” says Dombroskie.
It seems that almost every species of wasp or bee has its Batesian imitators. In addition to flies there are beetles and moths that resemble bees and wasps. Most of these mimics are harmless, Dombroskie says. “They can’t sting. They will act like they can. If you grab them they’ll buzz and be quite intimidating.”
There is, for instance, an almost perfect mimic of a bald-faced or white-faced hornet, a species that has a well-deserved reputation as a “vicious stinger,” says Dombroskie. On insect walks, he sometimes plays a little entomological joke on his entourage, pretending the mimic is a hornet and popping it in his mouth. “It freaks people out,” he says gleefully.
While mimics can fool you at first glance, there are ways to tell the real from the pretend. In the case of flies, they have two wings to a bee’s four. And while a bee’s antennae are crooked in an elbow shape, flies have short, or very fine, antennae. Behavior provides clues as well. Bees, hard workers that they are, move purposefully from flower to flower, while hoverflies, well, hover, and move erratically, zipping here and there. In the case of beetles that mimic bees, you should be able to pick out the beetle’s elytra, or the hard shell of the overwing. And in the case of bee-mimicking moths, including many of the hawk moths, their overlong proboscis is a clue.
While the mimics are frauds as stinging insects, when it comes to pollination, most are the real thing. Hoverflies, like my friends’ drone flies, are considered to be important pollinators, though exactly how important is not really known. Pollination research has been concentrated on bees. Dombroskie notes that flies may not be as efficient at pollination since they tend to be generalists, visiting a variety of flowers, while bees tend to concentrate on one type at a time. But they’re still out there helping plants spread their genes.
Joe Rankin keeps honey bees and writes on forestry, natural history, and sustainability at his home in central Maine. The illustration for this column was drawn by Adelaide Tyrol. The Outside Story is assigned and edited by Northern Woodlands magazine and sponsored by the Wellborn Ecology Fund of New Hampshire Charitable Foundation: firstname.lastname@example.org