Have you observed increasing mud (dirt) dauber nests around a dock aeration compressor cabinet, or outbuildings?  It doesn’t take long for them to become housekeeping nuisances and even damage facilities.

A customer reported $275 damage to trolling motors after the critters filled them with mud.  He later experienced

Mud Dauber

Mud dauber (Sceliphron caementarium) with a load of mud, just before takeoff. Courtesy of Wikipedia.

significant expense to repair an ATV after daubers blocked airflow to the motor.  They’ll build a nest in any nook or cranny. Annoying mud dauber nests are one of those “symptoms” we discussed in a recent newsletter.  If you’re fighting this battle, we’d wager you’ve noticed numerous spider webs.  Guess what daubers pack in their mud cocoons for developing larvae to eat.  You’re right, spiders.

This wasp group is named for nests made from mud collected by females. Mud is rolled into a ball, carried to the nest, and molded into place with mandibles. There are three different wasps that practice this behavior. The black and yellow mud dauber builds a series of cylindrical cells that are eventually plastered over with mud to form a smooth nest about the size of a fist.  Females prey upon all spiders, especially black and brown widows.  They likely appear in your area after finding a bug bonanza.  Instead of stocking one or two large spiders, they prefer particular types and sizes.  Two dozen small ones may be crammed into one nest cell.  They appear to know exactly what they’re hunting and where to find it.  After completing mud nests, females capture several insects or spiders to provision cells. Prey are stung and paralyzed before placed in the nest. A single egg is deposited on the prey within each cell and the cell sealed with mud. After finishing a series of cells, she departs and does not return.  Larvae that hatch from the eggs feed on prey items left by adults.  New adults emerge to start the process over again.

Wasps usually evoke a great deal of anxiety or fear. However, solitary wasps such as the mud daubers do not aggressively defend their nest like social wasps such as hornets and yellow jackets.  Mud daubers are very unlikely to sting, even when thoroughly aroused. They may sting if mishandled.  Except for making a big unsightly mess, mud daubers should be regarded as beneficial, since they remove and prey upon many spiders most people find disagreeable. Mud nests can be scraped off and discarded at night if they are objectionable, or wasp and hornet aerosol sprays can be used to treat nests if desired.  There is no proven method that is effective in discouraging wasps from building nests in sheltered or protected areas. Prompt and frequent removal of nests is suggested in areas favored by the wasps.  Scraping away nests only eliminates half the problem.  They’ll build it back almost overnight.  Complete treatment requires application of Viper insecticide or similar product.  Eradicating the spider population should send daubers in search of new feeding territory.