Mud Masterpieces

Solitary wasps are among the most amazing architects in the animal world, many of them creating beautiful nests in clay and sand. Each such dwelling will house a single offspring, provided with food in the form of paralyzed spiders, or insects of one sort or another. Sometimes more than one cell is created and the resulting multi-unit residence can be quite astonishing, too.

Perhaps my own personal favorites are the “potter wasps” in the family Vespidae, genus Eumenes. Females craft exquisite urns about the size of a marble, but usually complete with fluted “neck.”

She finishes one of these containers in its entirety before going off to hunt small caterpillars. She paralyzes several and stocks the pot with them. She then lays a single egg inside the clay sphere and seals the top with a final plug of mud. Inside, a larva hatches from the egg to find fresh food (paralyzed victims do not spoil like dead ones would). Once it has fed and matured, the larva molts into the pupa stage, and an adult wasp hatches a few weeks later, if the pupa is not overwintering for a longer period. The new adult chews a large exit hole in the side of the pot, crawls out, and flies off.

More commonly seen than potter wasp pots are they clod-like structures build by the black and yellow mud dauber, Sceliphron caementarium, in the family of thread-waisted wasps (Sphecidae).

The nests of this wasp are usually a cluster of several cells all covered in additional layers of mud. Some nests can be quite weighty, and thus are usually adhered beneath rock overhangs, or plastered under bridges and other man-made structures. Only one female is responsible for each nest, stuffing each cell with paralyzed spiders as food for the larva in each cell.

Another spider hunter is the aptly-named “pipe organ mud dauber,” Trypoxylon politum, family Crabronidae, found throughout most of eastern North America. Each female normally fashions two or more adjacent mud tubes, again adhered to a flat surface.

Each tube is actually a series of cells arranged in a linear fashion, partitioned on the inside. Trypoxylon are also spider-hunters, but in T. politum, they often work in pairs, male and female. While the female hunts or gathers mud, the male stays at home to defend the nest from potential parasites, predators, and rival wasps looking to usurp the rightful owners. The male has a wicked-looking hook on the underside of his abdomen that may help anchor him to the nest or substrate while doing battle. New nests of T. politum will be intact, while old nests will have large round exit holes down the length of each tube.

There is one other group of spider-hunting wasps that are accomplished masons. Spider wasps in the family Pompilidae, tribe Auplopini, construct delicate mud barrels to hold their spider prey and larval offspring.

Those in the genus Auplopus are small, with a widespread distribution. Phanagenia bombycina is a slightly larger wasp found east of the Rocky Mountains. Ironically, these wasps often build their mud cells inside the old nests of the pipe organ mud dauber.

Many people destroy the mud nests of wasps when they find them attached to their own home. They think the nests are an eyesore at best. Please consider tolerating them instead. Once finished constructing their nest, the female wasp goes off to build another somewhere else. She won’t “attack” even while building her nest. Solitary wasps are not at all aggressive like social wasps.

Those of you more scientifically inclined might consider “rearing” mud nests that you find. While you usually know what species will come out of one, there are many species of parasites that could emerge instead. Host-parasite relationships are not terribly well known, and you could make a significant contribution to science.