Masters of Mud: Auplopus Spider Wasps

The first image in this post is not of the insect I will be discussing today. That is because I am far more frequently asked what these little mud barrels are, and what makes them. Indeed, you are more apt to stumble upon these nests than you are to see their maker. While most spider wasps in the family Pompilidae dig burrows for their nests, or exploit pre-existing cavities, those in the genus Auplopus create free-standing mud cells.

I have few images of these wasps, and detest “stealing” images from others for my posts even though I give full credit when I do, so I hadn’t done an entry about Auplopus until now. It took a Facebook post by Eileen Miller to remind me that I was overdue to address them. Eileen was kind enough to share her own images in exchange for learning more about the wasps and their nests.

© Eileen Miller

There are ten recognized species of Auplopus in North America, but the genus is in dire need of revision. Collectively, the genus occurs across the entire continent. One species, A. carbonarius, is introduced from western Europe, and has been documented in New York and Michigan, but probably has a wider distribution in the U.S. than is currently known.

Several species are bright metallic blue-green, and the females at least are basically inseparable externally. Males can be identified by differences in the genitalia. Auplopus are small, averaging about 10 millimeters in length. Females have an oval spot on top of the abdomen near the tip called a “pygidial plate” that they use like a masonry trowel to manipulate mud pellets into segments of their mud nests. The female curls her abdomen beneath her during such work, so that the pygidial plate can contact the mud.

© Yurika Alexander via Bugguide.net Auplopus mellipes female

The nests are usually constructed inside pre-existing cavities in wood, or at least in sheltered niches such as under bark on standing trees, crevices in rock walls, or even inside the abandoned nests of other wasps like Sceliphron caementarium (Black and Yellow Mud Dauber), Trypoxylon politum (the Pipe Organ Mud Dauber), and paper wasps (Polistes spp.). The tiny barrel-shaped cells are roughly 15 millimeters in length and 7-10 millimeters wide, often stacked end-to-end, two to five per row.

Nest inside hole where a bolt used to be

The wasps appear to be mostly opportunistic hunters of spiders that do not spin webs.

Documented prey includes spiders from thirteen different families: Crab spiders (Thomisidae), jumping spiders (Salticidae), sac spiders (Clubionidae), ground sac spiders (Trachelas sp. in Corinnidae), ghost spiders (Anyphaenidae), longlegged sac spiders (Cheiracanthium sp. in Miturgidae), ground spiders (Gnaphosidae), nursery web spiders (Pisauridae) being the usual victims of North American Auplopus.

© Marie L. Schmidt via Bugguide.net Female wasp with spider prey

Adult or immature spiders may be taken, and the wasps usually amputate several, if not all, the legs of their prey. This allows the wasp to feed on the blood of the spider, but also facilitates easier transport of the victim over the ground. Presumably, more than one spider is placed in each mud cell before the female lays an egg on the last victim and then seals the cell.

© Eileen Miller, inside of cell showing pupa in cocoon

In at least one species, the emerging adult wasp regurgitates liquid to soften the mud cap on its cell, allowing it to more easily chew its way to freedom.

Auplopus seldom visit flowers, but can often be found around aphid colonies on honeyvine milkweed (Ampelamus albidus, Cynanchum leave), sunflower, and other plants. They feed on “honeydew,” the sweet liquid waste products that aphids secrete.

© Eileen Miller

Look for these little wasps from May to October, but especially July through September when they are most abundant. It should be noted that other Hymenoptera make very similar mud nests, particularly some of the Osmia mason bees, and some mason wasps (family Vespidae, subfamily Eumeninae). Auplopus are surprisingly well-studied insects, but information is scattered over articles in many different scientific journals and books.

Sources: Eiseman, Charley and Noah Charney. 2010. Tracks & Signs of Insects and Other Invertebrates. Mechanicsburg, Pennsylvania: Stackpole Books. 582 pp.
Evans, Howard E. and Carl M. Yoshimoto. 1962. “The Ecology and Nesting Behavior of the Pompilidae (Hymenoptera) of the Northeastern United States,” Misc. Publ. Entomol. Soc. Am. 3(3): 66-119.
Krombein, Karl V. 1967. Trap-nesting Wasps and Bees: Life Histories, Nests, and Associates. Washington, DC: Smithsonian Press (Publication 4670). 570 pp.
Kurczewski, Frank E. 1989. “Observations on the Nesting Behavior of Auplopus caerulescens subcorticalis and Other Auplopodini (Hymenoptera: Pompilidae),” Gt. Lakes Entomol. 22(2): 71-74.
Kurczewski, Frank E. and Mark F. O’Brien. 1991. “Auplopus carbonarius, a Palearctic Spider Wasp, Extends its Range to Michigan (Hymenoptera: Pompilidae),” Gt. Lakes Entomol. 24(3): 185-186.
O/Neill, Kevin M. 2001. Solitary Wasps: Behavior and Natural History. Ithaca, New York: Comstock Publishing Associates (Cornell University Press). 406 pp.

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.