A lot of people are alarmed by these creatures, batting and ducking and squealing when they fly too near. In fact, there is little to fear from mud daubers. They have the capacity to sting, but they aren't aggressive. Chances are good that even if they land on you, they will rest, not sting. Some people who are familiar with them will actually allow mud daubers to climb aboard a finger, where the insect ambles around contentedly without recourse to violence.
The mud daubers you see flying around are the females. They build nests for their larvae using mud. They prefer clay, but they will use whatever dirt they can find. The pipe organ mud dauber gets her name from her architecture. The tubes for the larvae cells she makes are long and dressed side-by-side like the pipes for an organ. Mud daubers find the edge of a body of water, pick up a small piece of wet soil with their legs and mouth, roll it into a ball and transport it back to the nest where it is packed on with precise symmetry.
Mud daubers do not rely on superfecundity to survive as a species. That means they don't produce a large number of offspring and play the odds that some will survive. One female typically produces about 15 eggs in her lifetime. Each mud cell in the nest contains only one larvae that which will become a pupae in three weeks, then cocoon until spring before it opens. The reproductive strategy is one of care, concealment and protection.
Mud dauber nests are considered unsightly on houses; and the fear of poorly understood insects is another motive for tearing down the nests. If you have to get rid of the nest, do not spray poison on it. That is dangerous to you, and scraping off the nest with a putty knife is safe and effective. Think hard before getting rid of them, though. Mud daubers feed their larvae only spiders. Blue mud daubers attack almost exclusively black widow spiders. The spiders are stung and paralyzed, then stuffed into a larva cell where they become food for the developing larva inside. Leaving mud daubers in place will keep your spider population in check during the summer.