Missouri's Mud-daubers

When I was young, I spent summers working on Cletus Zenk’s farm in Michigan baling hay, laying tile, painting fences, “fittin’ up” barns and savoring long, heavy lunches prepared by Clete’s wife, Pat. After one of Pat’s more memorable efforts, I rested my head against the shady side of an aluminum shed and dozed off until a painful, vibratory buzzing similar to that of a dentist’s drill jarred me back to consciousness.

Startled, I jumped up and poked my head through the doorway to see what was making the noise. On the other side of the thin aluminum, directly behind where my head had been, a delicate mud tube hugged the wall and joined three others that were more lightly-colored. It was an artistic display of small-scale masonry. The buzzing came from within one of the tubes. I bent down to look just as a shiny, bluish, white-footed wasp came out to meet me. For a split-second it danced in the air inches from my face, legs dangling—apparently studying me—and then it was gone.

It was a mud-dauber. It took me aback at first, but these harmless wasps and their mud-loving kin have fascinated me ever since.

Nest building of any kind is uncommon in the insect world. Most insects (butterflies, moths, many flies, many aquatic insects, many beetles and others) deposit eggs without much preparation or protection on plants, on leaf litter, on the soil, in the water or elsewhere. The young are left to fend for themselves. Other insects (katydids, cicadas, some beetles, parasitic wasps and others) give their young a bit of a head start by depositing eggs in plant tissues, rotten wood, in the soil and in living hosts.

Most nest-making insects, on the other hand, put considerable effort into selecting and building nest sites, renovating existing cavities or creating new ones. Also, they either passively or actively provide food and protection to their offspring. This kind of care and preparation increases the next generation’s chances of survival.

Missouri’s nest-making insects include many wasps, as well as most bees, ants and termites. In nearly all cases, the females build the nests and provide for the young. Most are “excavators,” digging sometimes elaborate tunnels, galleries and cells in the ground or in rotten wood. Certain wasps and bees, however, are like many species of birds in that they locate, collect and carry nesting materials to their nest site, creating a structure where previously there was only empty space. Most species subdivide the nest into individual cells in which food is provided and an individual egg is laid.

The very familiar social wasps (paper wasps, yellow-jackets and bald-faced hornets) create paper nests from chewed-up wood mixed with their saliva. Honeybees and bumblebees secrete wax as their main construction material. Some solitary wasps and bees use plant resins and other plant parts as construction material, but others, notably our mud-daubers, use mud as their material of choice. To an insect, it must seem like concrete.

“Mud-dauber” is a term used by entomologists to refer to several groups of solitary wasps in the family Sphecidae (the family in the order Hymenoptera that includes the cicada killer, sand wasps, and others). The three species of mud-daubers most commonly found in Missouri are the black-and-yellow mud-dauber, the blue mud-dauber (a second species of blue mud-dauber is not as common), and the pipe-organ mud-dauber, which was named by well-known insect observer, Missourian Phil Rau.

These three species of Missouri’s true mud-daubers are large and conspicuous. They are strongly attracted to barns, buildings, bridges and other structures as nest sites. In fact, these are the most dependable spots to find these wasps. Like chimney swifts and a few other animals, these true mud-daubers have adapted to, and seemingly benefit from, the presence of human structures.

Some smaller, less conspicuous Missouri wasps, including potter wasps and their relatives; a few spider wasps and some other sphecids, also use mud to build nests. Several common, widespread solitary bees, such as the blue orchard bee, also build mud nests.

Mud-daubers and their kin obtain mud in two ways. Some shape pellets from a mud source and carry them in their mandibles and forelegs to the nest site, where they work the mud into their nest. This is the method used by black-and-yellow mud-dauber, pipe-organ mud-dauber and several bees, among others.

The alternative method, “water-carrying,” is used by blue mud-daubers, most potter wasps and at least one bee. These species drink water and regurgitate it at a dry site, where they mix it with dirt to make mud. They then fly the mud to their the nest site. Blue mud-daubers actually make the mud at the nest site.

Mud-daubers and their relatives build nests quickly. During warm and sunny conditions, they may build several in a day.

They work the mud with their mandibles, mouth parts and legs. The organ-pipe mud-dauber and the black-and-yellow mud-daubers often “sing” (vibrate or sonicate) while spreading mud, and sometimes when collecting it. Presumably, the vibrations help distribute the mud evenly. The mud-daubers visit the same mud and water sources repeatedly, but different shades of “mud brown” can be seen on most nests.

Black-and-yellow mud-dauber build a simple, one-cell, urn-shaped nest that is attached to crevices, cracks and corners. Each nest contains one egg. Usually, they clump several nests together and plaster more mud over them.

Blue mud-daubers frequently appropriate old nests of black-and-yellow mud-daubers. They carry water to them and recondition them for their own purposes. The two species commonly occupy the same barns, porches, or other nest sites.

Organ-pipe mud-daubers build their very distinctive and elegant tubes on vertical or horizontal faces of walls, cliffs, bridges, overhangs and shelter caves or other structures.

All three species may occupy the same sites year after year, creating large numbers of nests. Mud-dauber nests can last many years in protected locations and are often used as nest sites by other kinds of wasps and bees, as well as other types of insects.

Like most other wasps, mud-daubers are predators. The females not only build the nests, but they hunt to provision them. However, pipe-organ mud-dauber males have reportedly brought spiders to the nest, and they aid in nest-guarding.

Adults of both sexes frequently drink flower nectar, but they stock their nests with spiders, which serve as food for the mud-daubers’ offspring. Like connoisseurs, they prefer particular kinds of spiders, and particular sizes of spiders for their larders. Instead of stocking a nest cell with one or two large spiders, mud-daubers cram as many as two dozen small spiders into a nest cell. They appear to know exactly what they are hunting for, and where to find it.

Black- and -yellow mud-daubers primarily prey on relatively small, colorful spiders, such as crab spiders (and related groups), orb weavers and some jumping spiders. They usually find them in and around vegetation.

Blue mud-daubers prefer immature black widow spiders and their relatives. They hunt them in dry areas, such as outbuildings, rocky areas and stone piles.

Pipe-organ mud-daubers generally provision their nests with various kinds of orb weavers, but their diet includes other kinds of spiders, as well.

To capture a spider, the wasp grabs it and stings it into submission. The venom from the sting does not kill the spider, but paralyzes and preserves it so it can be transported and stored in the nest cell until consumed by the larva. A mud-dauber usually lays its egg on the prey item and then seals it into the nest cell with a mud cap. It then builds another cell or nest. Missouri’s mud-daubers generally have two generations per year. The young survive the winter inside the nest.

One disadvantage to making nests is that most, if not all, of the nest-maker’s offspring are concentrated in one place, making them highly vulnerable to predation. Once a predator finds a nest, it can plunder it cell by cell. A variety of parasitic wasps, ranging from extremely tiny chalcidoid wasps to larger, bright green chrysidid wasps attack mud-dauber nests. They pirate provisions and offspring as food for their own offspring.

The muddy nests of mud-daubers are an occasional nuisance to some homeowners, but the wasps themselves are not aggressive or dangerous. However, they will sting if handled. A trowel and a hose can be used to remove old nests.

Observing a mud-dauber nest is an interesting and rewarding experience. It’s also an effective way to learn patience and refine observation skills. The behavior of these interesting native insects can be observed very closely, but—as was my experience—the wasps may observe you in return.