Dirt-Dauber Wasps


Many folks know the nest of the dirt-dauber or mud dauber wasp. The long cylinders of mud, 6 inches or so in length, are usually constructed in protected areas such as inside barns or under house eaves. Because several slender cylinders are constructed side by side, the completed nest looks like a bank of organ pipes. Although only used by the wasps for one summer, the nests may persist for years.

As the wasp builds the nest, it carries small balls of clayey mud in its legs to the nest, then molds each dollop of mud with its mouth and legs to the right shape. Often, it also vibrates its wings and buzzes, perhaps to dry the clay into pottery or even to help shape it. It has been suggested that the vibration of the wasp’s wings is attuned to the resonant frequency of the mud, so that the mud picks up the vibration the same way a guitar string will hum with the sympathetic vibration from a correctly pitched voice. So much of nature is harmonic!

If you’ve ever removed an active dirt-dauber nest and looked inside, you may have noticed that the cylinders are made of several chambers, each of which is packed with spiders. Most people squeal, drop the nest and take off at this point, but the story gets even more macabre.

The spiders are alive, but are paralyzed. Some of them will weakly move their legs, but none can crawl. And now for the worst of it—entombed inside each section of the nest with several living, helpless spiders, is one wasp egg. When it hatches, the wasp larva will begin to eat the spiders, one by one. The spiders are kept alive so that they are fresh, ready for the larva to eat when the time comes. Similarly, sailors used to fill their ships with Galapagos tortoises, turned upside down to keep them helpless, so that the crew would have fresh meat during their multi-year journeys.

If you are really observant, you might even see the wasps hunting for their prey. Different species of wasp prefer different species of prey. Some hunting wasps select only spiders that live on the forest floor, others prefer spiders that build webs in the open, and one western species specializes on tarantulas! Other hunting wasps eat caterpillars, crickets, cicadas, or aphids instead of spiders. Most of the hunting wasps look very similar—they are blue-black and slim-waisted, and flutter their wings as they hunt. In addition to mud daubers, potter wasps also use mud to build their nests, but construct tiny pots instead of pipes. Others, such as the more colorful cicada killers, dig nests in the ground, and still others, such as the aphid wasps, bore into wood.

The battle between a wasp and a spider can be dramatic because they are of similar size. The wasp leaps on the spider, and often they tumble around together, rattling the dried leaves, as each tries to gain the advantage. Usually the wasp succeeds in stinging the spider, which then goes limp. Often the spider is so large that the wasp must drag it across the ground or fly in short hops to its nest.

Another group of strange-looking wasps that are common this time of year have a similar natural history. These wasps, called ichneumonids and pelecinids, have very long, skinny abdomens. Their prey is the larvae of beetles, and the long abdomen is used to penetrate either wood or soil, depending on where the beetle grub lives, and place the wasp egg onto the body of the beetle larva. When it hatches, the wasp larva eats the beetle grub.

So next time you see a wasp, watch it for a while and you might see something of its hunting behavior. Hunting wasps rarely sting, so there is no need to destroy the nests of dirt-daubers. You can stand right by the nest and watch as the mother wasp brings in spiders to fortify her children.

Nest of Dirt-daubers


Copyright 2003 by Jennifer E. Frick

Text and photos may not be used without permission of the author