The organ pipe mud dauber wasp

They don’t need much — a dry, sheltered spot out of the sun, a smooth, vertical surface, a nearby forest, a handy source of mud and a healthy supply of spiders. These are the requirements sought out by the organ pipe mud dauber wasp (Trypoxylon politum). Belonging to a group known as square-headed wasps, this is the only North American species in the genus Trypoxylon that creates its own, free-standing mud nests.

Organ pipe mud dauber wasps are beautiful shiny black insects, with a tiny bit of white or pale yellow on the final section of their back legs which hang down beneath a very diminutive waist. They are a good size, ranging from 1.5 inches to 2 inches in length and are active from May to September when the females are busy constructing their long, mud tubes in neat rows of five or six. These structures and the way they are organized side by side give the appearance of organ pipes. Yet it is the architecture and function of these nest chambers that provide fascination.

Building nest chambers

Once a site has been carefully chosen, the female gets to work. Collecting a ball of mud from a moist area nearby, she begins construction by building a chamber, or cell. Once the first cell is complete, she sets out in search of a spider.

Organ pipe mud daubers feed on three genera of spiders, all of them orb weavers. When the female locates a spider of the correct size and species, she stings it, just enough to paralyze it, but not kill it. She places the stunned spider inside the cell, emitting a loud buzzing sound as she does so, and, depending on its size and the amount of room remaining, she goes in search of another. As many as four spiders may be crammed into the space. Finally, she lays a single egg in with the spiders and seals up the cell with a mud partition then immediately goes to work, extending the pipe downward. Amazingly, one mud structure 8 inches long might contain a total of seven cells and 28 spiders. Multiply that by a group of six pipes the same length and you have up to 168 spiders.

While the female works, the male wasp stands guard, encouraging her and working to protect the nest site while she is away, sometimes even helping with the construction. But his main duty occurs after construction and egg laying is complete. In an act of “parental care,” he guards the nest against other males, parasites and various intruders. This act plays a huge role in the success of the young.

Hatching and growing

When the egg hatches, a tiny white larva emerges and finds its chamber stocked with fresh, live food. Slowly, it begins to eat the spiders whose space it shares, growing larger and larger. Finally, when its food source is used up, the larva, now as large as the cell itself, forms a brown pupa, much like that of a moth, and begins to metamorphosize into an adult mud dauber wasp. When the time comes, the newly formed wasp pushes out of its papery pupal shell and carefully chews its way out through the dry mud walls of its cell to freedom, leaving a telltale round hole in the side.

New female wasps begin to build nest structures within 48 hours after emerging. Chambers created late in the season will contain pupae that overwinter, and up to two generations of wasps are produced each year.

So, what’s not to like about organ pipe mud dauber wasps? Well, I suppose you could complain about the muddy mess they make when constructing their nesting chambers, say, on the siding of your house. Since they require a sheltered location, there is usually no rain to wash them off anytime soon.

The wasps themselves are extremely docile. Yes, they can sting, but will only do so in an act of self-defense if you catch one and squeeze it between your fingers or perhaps accidentally lean against an unsuspecting individual. The fact that they will never attack allows for an up-close, front-row viewing opportunity while they work. In addition, you certainly can’t ignore the fact that they play a large role in keeping the spider population down in the area of their nests.

Inspiration

I was spurred into writing this particular article because I found myself watching a female mud dauber busily building her nesting structures on our front porch right next to my swing. One thing I noticed while watching was that at the end of each day, there were always several stunned spiders lying on the ground beneath the tubes, ones which most likely were accidentally dropped.

One evening while I sat observing, a Carolina wren came shooting around the corner of the house, onto the porch and nearly ran right into me. The bird was obviously both surprised and irritated by my presence, as it sat on the railing, not 5 feet away, scolding me at the top of its lungs. I knew there was no nest nearby, and I was perplexed by the behavior. Interestingly, the same encounter happened the following evening at almost the same time and this time, a little light went on inside my head. Slowly, I backed away to the opposite end of the porch and watched as the little bird dropped down and gobbled up the paralyzed spiders beneath the wasp’s nest. I learn something new every time I write this column. Who would have thought that these beautiful insects could be playing such a big role in the dinner menu of these tiny birds? The web of life is more complicated than we will ever know. Remember, just because something isn’t benefitting us personally, doesn’t mean that it isn’t extremely important to something else!

Video

To view a couple of slow-motion videos shot on my front porch, visit my YouTube channel links at youtube.com/watch?v=xlrHBFgdOPQ and youtube.com/watch?v=_OB2AP6mQu8.