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Bug of the Week is written by "The Bug Guy," Michael J. Raupp, Professor of Entomology at the University of Maryland.

Where have all the spiders gone? Black and yellow mud dauber wasps, Sceliphron caementarium


A beautiful black and yellow mud dauber prepares to gather mud at the water’s edge of the mighty Shenandoah.  Photo credit: Paula Shrewsbury


Exit holes mark emergence sites of mud daubers that have completed development within mud nests constructed by their mothers.


On a steamy day in Maryland, nothing beats a trip to one of our mighty rivers, the Potomac or the Shenandoah. After a fierce hike on a scorching day, I stopped by the Shenandoah at Harper’s Ferry to cool my hot feet. Along the riverbank dozens of mud daubers discovered what must have been the perfect formulation of clay, minerals, and water to construct pottery homes for their young. In an amazing display of harmonized movements, mouthparts and legs of mud daubers formed spheres of glistening mud and airlifted mud balls to nearby human-made structures. Corners of window frames and doorjambs are perfect locations out of the rain to build pottery homes for their young.




Watch as mud daubers use clever jaws and legs to shape mud into perfect balls ready to be airlifted to the nest construction site.

Several juicy paralyzed spiders await the hungry jaws of a mud dauber larva inside their clay crypt. 

Nest construction by Sceliphron caementarium centers on creating a series of hollow mud chambers, provisioning each chamber with food, depositing an egg in each chamber, and then sealing the mud tubes with a cap of mud to keep out weather, but more critically to also exclude parasitoids and predators intent on making a meal of mud dauber larvae. Just what are the provisions for babes of black and yellow mud daubers? Spiders, lots of them. Individual cells of mud daubers may contain as many as 25 spiders to serve as food for a single wasp larva. Several species of web spinning and hunting spiders have been discovered stowed away in nests of mud daubers.

After provisioning all the cells with spiders and laying an egg in each cell, a mud dauber puts the finishing touches on a nest.

One might think that spiders are pretty risky food for baby wasps but mother has a way to disarm these fanged prey. Female mud daubers deliver a venomous paralytic sting to the nerve center of the spider, rendering it immobile and harmless. These spiders are the ‘undead’. Sealed in clay coffins, the spiders will be consumed alive one by one by the developing wasp larva. When the last spidery zombie in the chamber is consumed, the wasp larva pupates and later emerges as an adult ready to find a mate, build mud nests, and capture spiders for young of her own.

Unlike the venom of hornets, yellow jackets or honeybees that is meant to inflict pain on vertebrates intent on robbing nests or hives, the venom of mud daubers is designed to paralyze prey and the sting of these docile wasps is reported to be mild by comparison, much like the sting of solitary bees we met in a previous episode. The primary concern raised by these beautiful spider hunters is the aesthetic disfigurement of buildings where clay nests stuck on walls, doorjambs, eaves, and window frames can be very abundant. In an interesting twist to this mud dauber story, workers cleaning up a nuclear waste facility apparently found wasps gathering radioactive soil to build their nests and many of their creations were “fairly highly contaminated” with radioactive isotopes. Just imagine giant mutated wasps glowing in the dark and capturing small pets instead of spiders to provision their nests! Sounds like reasonable grist for another B grade sci-fi movie about insects.


Balls of mud collected at the river bank are molded to form nests in protected spaces like door frames and support beams of railroad trestles.


Thanks to Paula Shrewsbury for inspiration and the lead photograph used in this episode. The wonderful Featured Creature Sheet “Common name: black and yellow mud dauber, scientific name: Sceliphron caementarium (Drury, 1773) (Insecta: Hymenoptera: Sphecidae)” by Erin Powell and Lisa Taylor and “Radioactive wasp nests at Hanford reservation” by the Associated Press were used to prepare this episode.