| The mud dauber is one of a few types of wasps that aren't particularly hostile. They're solitary insects that build small nests out of mud in or around homes, barns, and other structures.
They are long, slender wasps with thread-like waists. The name of this wasp group comes from the nests that are made by the females, which are made from mud molded into place by the wasp's mandibles. There are three different species of mud daubers with distinct coloring: the organ-pipe mud dauber (solid black coloring), the black and yellow mud dauber, and a stunning metallic-blue mud dauber with blue wings.
The organ-pipe mud dauber, as the name implies, builds nests in the shape of a cylindrical tube resembling an organ pipe. The black and yellow mud dauber's nest is comprised of a series of cylindrical cells that are plastered over to form a smooth nest about the size of a fist. The metallic-blue mud dauber, in a cunning display of laziness and downright coolness, foregoes building a nest altogether and simply uses the abandoned nests of the other two species.
After building a nest, the female wasp captures several spiders or insects. The captured prey are stung and paralyzed before being placed in the nest, and then a single egg is deposited on the prey within each cell. The wasp then seals the cell with mud. After finishing a series of cells, she leaves and does not return. Eventually, the hatching larvae will eat the prey and emerge from the nest.
The unique, and somewhat endearing, thing about mud daubers (and other solitary wasps) is that they very rarely, if ever, sting people or animals. Even when they're thoroughly agitated or aroused, they are not likely to sting.
By being very calm-tempered and helping control the insect and spider population, these wasps gain a lot of respect from people. Mud daubers are extremely common in rural Texas where I grew up, and killing one without reason was considered cruel and silly. Even when they built nests on our front porch, we didn't bother them, because they didn't bother us. They're nice wasps.
N0b0dy points out that sceliphron caementarium is the scientific name for the mud dauber. | 
