Potter wasps

A kinder, gentler wasp.

Eumenes fraternus: You can see her little round ball of mud held underneath her chin. - Matt Pelican

The Island boasts some fine ceramic artists, and some of them aren’t human.

Potter wasps are a division within the wasp family Vespidae, which also includes the more familiar bald-faced “hornet” (technically a wasp), yellow jackets, and paper wasps. All superficially similar, these insects have the classic wasp “look,” including a tendency to be marked with bands of bright color, usually yellow (potter wasps often get mistaken for yellow jackets).

The subfamily of potter wasps, Eumeninae, differs from its relatives in a number of minor anatomical traits. But the main distinctions, at least from the perspective of an amateur observer, are behavioral.

For one thing, potter wasps are far less aggressive than their better-known relatives (the aggressiveness even of our true stinging wasps is exaggerated in most people’s minds); it takes a grievous insult to get a potter wasp to sting you.

But most important, the nesting behavior of potter wasps distinguishes them from their relatives: rather than the paper nests built by colonies of our better-known wasps, potter wasps generally construct small, sometimes elaborate vessels made of mud.

While paper wasp and yellow-jacket nests are occupied by whole colonies, potter wasps are so-called solitary wasps, with each female building a nest entirely on her own. Potter wasp nests vary widely in shape and location; some are built underground, some are pasted to hard surfaces, and many are built on or around the stem of a plant. Each species has a distinctive design and preferred location, and if I knew what I was doing, I could often identify the species responsible for a potter wasp nest.

Each “pot,” when finished, receives a single egg laid by an adult female; in addition, the mother stocks the nest with one or more prey items, stung and paralyzed by the adult and left for the maturing wasp larva to feed on as it develops. With the “pot” loaded up with an egg and food, the adult wasp seals over the entrance and leaves her offspring to develop on its own.

Potter wasps, to some degree, specialize in the prey they hunt for their young. Most species take only caterpillars; some no doubt specialize in caterpillars of just one family, or even one genus. This dining preference makes these wasps one of the most beneficial of insects from the human perspective: Potter wasps are a powerful force controlling agricultural pests such as cutworms.

As fearsome as their reproductive habits make them sound, adult potter wasps themselves generally eat just pollen and nectar. Being much less hairy than bees, wasps in general are probably less efficient at carrying pollen than bees are. Still, potters spend a good portion of their time visiting flowers, and like other insects with this habit, they can surely help plants reproduce.

I imagine that building a potter wasp “pot” requires just the right kind of dirt, probably with a high percentage of clay in it. And the wasps of course have a knack for finding the right kind of raw material.

I recently watched several species of potter wasps visiting a small patch of finely textured sand that had been turned up by a snow plow last winter. Each wasp visited the sand patch, fidgeting with its front legs; I finally realized the fidgets were all about rolling up a small ball of soil. The sand was bone-dry and totally unpackable, but apparently the wasps moisten it to packability with regurgitated water.

Once an adequate ball of sand was constructed, the wasp would fly away, reappearing a few minutes later to take up another load. I never found any of the nests –— the wasps took off like rockets when they left with their mud balls –— and this would have been puzzling behavior indeed if I didn’t already know about the nesting habits of these insects!

It’s depressing to me that a web search for “potter wasps” turns up more exterminator websites than anything else. Sure, these wasps resemble their sting-ier cousins. And a few species of potter wasps may stick their nests to manmade structures, such as house siding or the undersides of eaves, though it’s actually mud daubers, in yet another wasp family, that seem to be responsible for most such nests on the Vineyard.

But it takes a mighty fastidious housekeeper to gripe about ceramic artwork embellishing a house. And when you weigh that minor inconvenience against the control of undesirable insects, the pollination services, the docile nature, and the fascinating behavior of this subfamily, potter wasps are clearly insects that should be encouraged, not exterminated.