A mason wasp is an insect related to bees and yellow jackets, belonging to a subfamily called Eumeninae. Most are subtropical species; the four-toothed mason wasp is the only one found north of south Texas.
There are about 30 species of mason wasp recognized, although the four-toothed mason wasp is the most studied; it can be taken as representative because it has much in common with its relatives. For example, like other mason wasps, it does not build its own nest. Instead, it resides in nests built by other animals, such as carpenter bees. It uses mud to build partitions in the tunnels it takes over, which biologists have likened to masonry. It is solitary and preys on other insects — especially caterpillars.