Mud Stories

The Lives and Trials of Mud Dauber Wasps

Mud nests constructed by mud dauber wasp, Trypoxylon politum. Note the variety of exit holes.

 

          Now and then, I get caught in a Florida rainstorm and duck under a bridge or overhang to escape the rain, and notice a set of mud tubes attached to the wall above my head.  Maybe you’ve seen such things too, but this is what I call a Found Object, a small thing that has a story to tell, a story that can be small or large, simple or complex.  This particular object reveals its story through a little detective work---- a female mud-dauber wasp that found a supply of mud nearby and carried gob after gob of mud to this wall to mortar it into a series of arches to form an elongated mud tube of simple elegance (extreme right tube).  She started with a red source of mud, but then discovered an apparently better grey source to finish most of the tube.  Whenever she had completed approximately a body-length of tube, she took a break to hunt web spiders.  She stung each spider into paralysis, and plucked it out of the web, flew it to the nest and stuffed it in.  After stuffing in 5 or 10 spiders, she laid an egg on the last spider, then walled the cell shut to continue making mortar arches until she had another body-size chamber, whereupon she repeated the spider hunt, chamber sealing and further construction until the tube contained five to eight filled cells.

            Having finished one tube, she might have commenced on another one attached parallel to the first, but this could easily have been a different female, for mud-dauber nests, for obvious reasons, are often aggregated in sheltered places.  Given the changes in mud color, the set of tubes pictured here was the work of multiple females over (perhaps) multiple years.

            But this is just the beginning of the story, for each cell has its own, often divergent story.  Inside each sealed cell, the wasp egg hatched, and the wasp larva began eating the paralyzed spiders (can you empathize with the spider, eaten alive?), eating the entire cache of spiders in five or six days, increasing the larva’s weight by 600%.  The larva then formed a stiff cocoon around itself and became a pupa inside it.  After a couple of weeks, the adult wasp that emerged from the pupa cut a circle off the end of the cocoon, like topping a soft-boiled egg, then cut a hole in the wall of the mud tube.  The twelve large holes indicate that at least twelve adult wasps emerged to start the cycle over.

            But life didn’t go as smoothly for some of the stocked mud cells. There were approximately 36 stocked cells, but only 12 large exit holes from which adult wasps emerged. Smaller exit holes are evidence that at least three cells fell victim to a parasitic sarcophagid fly that laid several eggs on the spiders while the female was out hunting more.  When the wasp female mudded the cell shut, the fly eggs hatched and the maggots indiscriminately devoured the spider and wasp larva, then pupated in the cell to emerge later from smaller exit holes. 

            Cells without exit holes could have had one of several fates--- the wasp larva died without consuming the spiders, the adult might have died in the cocoon, both sealed forever in their mud sarcophagus.  Alternately, the wasp larva grew but was then consumed bit by bit from the outside by a tiny parasitic wasp, Mellitobia chalybiae.  This parasite completes its life cycle inside the cell where brothers mate with sisters and produce more generations of the parasite until the host larva has been completely consumed and the cell contains scores of adult wasps and hundreds of cast cuticles.  Some of the female Mellitobia emerge through holes so tiny that they are hard to see and fly off to parasitize another mud-dauber cell. 

            This is still far short of the complete list of fates that can befall the mud-dauber’s work. There are bee-flies that hover in front of the still open cell to toss eggs into it while the mud-dauber is out hunting.  There are other mud-daubing spiders that steal the spiders from open cells, and beautiful, metallic green cuckoo wasps that parasitize the wasp larva.  And each these parasites can itself be parasitized by the sarcophagid fly or the mellitobia wasp--- parasites of parasites.  Fleas upon fleas.

            But even this is not the end of the story. Empty mud cells can be re-used by several species of cavity-nesting wasps and bees of several sizes.  Some use the empty mud-dauber cocoon as a handy home, stuff it with paralyzed spiders and an egg, then cap it with mud. Others remove the empty cocoon and remodel the cell into smaller apartments before sealing the entry hole with a different color mud.  If these little wasps emerge successfully, they breach the plug with a smaller hole, allowing another generation of smaller wasps to re-use the cell and to plug the breached plug with still another color mud.  And of course, each of these re-users is dogged by its own hovering parasites and predators, who in turn have theirs.  It is a whirling community of opportunists, all beginning with the construction of mud cells by a mud-dauber wasp.

            And when there is nothing living to exploit, the community’s janitors, skin beetles and their larvae move in to eat up stuff indigestible to other creatures--- bits of spider legs, cast cuticle, shriveled corpses and feces.  Eventually, the mud nests erode and degrade, or the first set is buried under later ones to form mud labyrinths spanning decades, an insect equivalent of an archeological site waiting to have its story told.