Mud-Dauber

A yellow-legged mud-dauber on the window of my truck. Notice the thin, elongated connection or pedicel between the middle and rear segments of the body.

In one of the first posts that I published on this blog, I talked about insect specialization and the relationship between insect and native plant diversity. Because herbivorous insects will often specialize on eating one particular species or group of plants, an area with a high diversity of native plants will also tend to have a high diversity of insects. In that same post, I also talked about how this relationship can be extended to the diversity of insect parasites, which also tend to specialize. Last week, while starting up the truck I use at work, a common and rather visually striking example of this process of diversification through parasitism landed on the driver-side window - a yellow-legged mud-dauber (Spheliphron caementarium).

The yellow-legged mud-dauber is a member of the Sphecidae family of wasps, appropriately known as the thread-wasted wasps due to the thin, elongated connection or pedicel between the middle and rear segments of the body. Their strange appearance and yellow and black coloration have inspired some nasty rumors about them being aggressive, but in truth they are pretty calm as far as wasps go. Adult mud-daubers are solitary, feed mainly on nectar, and you really have to put in some effort to get one to sting you. 

Like many sphecid wasps, yellow-legged mud-daubers are parasitoids. Unlike your standard parasites, whose entire life cycles occur at the expense of their hosts, parasitoids are free living as adults and only act as parasites when they are young. This reproductive strategy is actually very common among wasps, with the colonial yellow jackets and paper wasps that people typically know best being outliers in this regard. Like herbivores insects with their host plants, parasitoid wasps will often specialize on particular species or groups of invertebrates and only parasitize members of that group, resulting in significant diversification.

A yellow-legged mud dauber nest under construction. Each of the tubular structures or cells making up the nest will contain one egg and several spiders to feed the larva when it hatches. 

Spiders are the preferred hosts and targets of specialization for the yellow-legged mud-dauber. After she has mated, a female dauber will fly around collecting balls of mud which she will fashion into small cells for her young. Historically, mud-daubers would attach these cells to the ceilings of caves, rocky ledges, or crevices, but these days, you'll also find them in neighborhoods building nests on the sides of buildings or under the eaves of houses. This particular individual seems to have been building her nest on the side of the garage at work.

Once a cell is complete, the mud-dauber will go out hunting for a spider. When she finds one, the dauber does not actually kill the spider, but rather administers a paralyzing sting and brings it back to her nest, where she places it inside one the mud cells she has constructed with a single, fertilized egg. She may, at this point, seal up the entrance of the cell with more mud, and start building another one next to it, but more often, she will go out and collect more spiders, up to 25 for a single cell. When the egg inside the cell hatches, the larva will eat its way through the spiders, all of which are kept fresh because, remember, they are not actually dead, but paralyzed! Once the larva has eaten all the spiders and reached the appropriate size, it will pupate and turn into an adult, chewing its way out the mud cell to start the process all over again. 

Creepy, but pretty interesting!

Yellow-legged mud-daubers aren't the only wasps that target spiders as hosts for their young, but other species that do so will often specialize on different kinds of spider. Yellow-legged mud-daubers seem to prefer spiders in the family Thomisidae, a group which includes a number of species that ambush their prey by imitating the color and form of specific flowers (more specialization). The blue mud wasp (Chalybion californicum), on the other hand, seems to have a preference for black widows. The two species also differ in their hunting method, at least for spiders that build webs. When a yellow-legged mud-dauber comes across a spider on a web, she will slam against the web so that the spider falls to the ground and will proceed to catch it there. The blue mud wasp, meanwhile, will land on the web and imitate the movement of trapped prey, then sting the spider when it approaches (Blackledge and Pickett 2000). 

In addition to parasitizing spiders when they are young, adult blue mud wasps also have a parasitic relationship of sorts with yellow-legged mud-daubers, whose nests they will often take over and use for themselves. They do this by collecting water and using it to moisten the wall of a cell until it destabilizes. They then remove both the egg and the spiders placed inside the cell by the mud-dauber and replace them with their own egg and spiders, before sealing the cell back up again (Rau 1928). As if this isn't enough for the mother yellow-legged mud-daubers to worry about, there is another parasitoid wasp, the introduced cuckoo wasp Chrysis angolensis, which uses larval mud-daubers in the genus Spheliphron as hosts for its own offspring (Ratzlaff et al. 2016). Like the blue mud wasps, Chrysis angolensis will break into a mud-dauber nest to lay its eggs, but will not discard the mud-dauber eggs or the spiders collected by the dauber, instead leaving them both inside to be devoured by its own growing larva.  

To sum up then, we have a chain of diversity that begins with a variety of plants each spinning off a set of specialized herbivorous and (perhaps) camouflaged Thomisid spiders which feed upon those herbivores. The spiders are in turn parasitized by the specialized yellow-legged mud-daubers, which are parasitized by the blue mud wasp (also a specialist of black widow spiders) and the cuckoo wasp Chrysis angolensis. We could probably go further, looking at what kinds of microbes might be specifically adapted to living on or in the blue mud and cuckoo wasps for example, but we'll leave it there for now. The point is that each new species of plant, insect, and spider produces an opportunity for yet another specialist to feed on or parasitize it. Nature arbores a vacuum and yet, each time it fills one, it creates many more. Life grows and skuttles, buzzes and swims until, the next thing you know, a planetary lifetime has passed, and we are counting species in the millions. 

Sources:

Blackledge, T. A., & Pickett, K. M. (2000). Predatory interactions between mud-dauber wasps (Hymenoptera, Sphecidae) and Argiope (Araneae, Araneidae) in captivity. The Journal of Arachnology, 28(2), 211-216.

Chatfield-Taylor, W. (2022)). Species Chrysis angolensis. BugGuide.net. https://bugguide.net/node/view/243038 

Missouri Department of Conservation (N.A.). Mud Daubers. Field Guide. https://mdc.mo.gov/discover-nature/field-guide/mud-daubers  

Ratzlaff, C. G., Needham, K. M., & Scudder, G. G. E. (2016). Notes on insects recently introduced to Metro Vancouver and other newly recorded species from British Columbia. Journal of the Entomological Society of British Columbia, 113, 79-89.

Rau, P. (1928). The nesting habits of the wasp, Chalybion caeruleum. Annals of the Entomological Society of America, 21(1), 25-35.

Texas Apiary Inspection Service (N.A.). Mud daubers. Texas A&M AgriLife Extension. https://txbeeinspection.tamu.edu/mud-daubers/

The Bug Lady (2011). Black and yellow mud dauber (Family Specidae). University of Wisconsin Milwaukee Field Station. https://uwm.edu/field-station/black-and-yellow-mud-dauber-family-specidae/