While trimming weeds around a field stone enclosed flower bed, I noticed a small earthenware vessel attached to the side of a stone. Having seen these before attached to walls, twigs and leaves, I knew I had discovered a real delight, the brood chamber or “pot” of a potter wasp. The adult potter wasp obtains nutrients from the nectar and pollen of flowers. But when not on the hunt for a snack, potter wasps are busy constructing homes for their young and provisioning them with food. This home is the curious pot from which the potter wasp gets its name.
The female potter wasp gathers clay and soil particles in moist areas and transports them back to the construction site, which in this case was a stone wall. Layer by layer she carefully molds the mud into a tiny hollow vessel. This requires many trips to the mud puddle. When the pot is nearly finished, but before it is sealed, the potter wasp completes two important tasks. First, she provisions the pot with enough food to support the growth and development of her youngster that will grow inside the pot. In the case of the potter wasp in my garden, the larder consisted of several rather small caterpillars in shades of green and brown. The almost fully grown larva had clearly eaten several caterpillars and four still remained when I opened the pot. Other potter wasps fill their pots or earthen galleries with beetles or spiders that will be food for their young. Upon finding a caterpillar the potter wasp delivers a paralyzing but non-lethal sting, and then carries the victim back to the pot where it is interred.
When the pot is fully stocked with fresh meat, the potter wasp takes care of the second important task of depositing an egg on the unfortunate victims. To keep her youngster safe, the potter wasp gathers more mud and seals the chamber completely. After a few days the egg hatches into a small legless larva. How clever an adaptation, paralyze but don’t kill caterpillars so the undead remain unspoiled while they await the hungry jaws of the wasp larva. Surrounded by food and protected from most of its enemies inside the pot, the larva grows and develops as it eats the nutritious caterpillars. When the cupboard is empty and the larva is fully developed, it molts into a pupa and transforms from a legless mass of flesh into a spectacular wasp. With powerful jaws the wasp breaks open its earthen nursery, frees itself, and emerges to find a mate. It then undertakes the tasks of gathering mud, capturing caterpillars, and building a little pot for its own offspring. I have read that these tiny pots may have inspired pottery designs used by Native Americans. Eumenid wasps are among the most diverse of all members of the vespid wasp clan. As the goldenrods and late summer plants begin to bloom, keep an eye open for these not so scary potters who help rid your garden of pesky caterpillars.
My mint plant provides a tasty morning meal for this pretty potter wasp.