The blue mud dauber is a metallic blue species of mud dauber

Mud dauber

Mud dauber is a name commonly applied to a number of wasps from either the family Sphecidae or Crabronidae that build their nests from mud...

 wasp that preys primarily on black widow spiders. It does not build a nest, but uses nests abandoned by other mud dauber wasps. Like other mud daubers, it is rarely aggressive. Blue mud dauber wasps are generally considered beneficial, because they help to regulate the population of black widow spiders.