Wasp, common name applied to most species of hymenopteran insects, except bees and ants. Insects known as wasps include the sawflies, the parasitic wasps, and the stinging wasps, which are the best known. About 75,000 species of wasps are known, most of them parasitic.

Wasps are characterized by two pairs of membranous wings and an ovipositor (tube for laying eggs) that may be modified in various ways. In some species one sex may be wingless. In the vegetarian sawflies, the abdomen is broadly attached to the thorax and the ovipositor is rigid; in the higher wasps, the abdomen is flexibly attached to the thorax and the ovipositor is movable. The larvae of parasitic wasps consume the bodies of other insects or, in a few cases, consume plant tissue. Most stinging wasps are predators or scavengers; their ovipositors may be modified to inject venom used for killing prey or for defense.

Unlike social wasps, sawflies and parasitic wasps are free-living-that is, they do not build nests. After depositing their eggs on a host plant or animal, the adult wasps fly off in search of food for themselves or more hosts for their larvae. The eggs are left to develop and hatch on their own. However, some stinging wasps live in societies that are more complex than those of social bees and ants.
The stinging wasps rely on a nest from which they conduct many of their activities, especially rearing young. Wasp nests may be as simple as a straight burrow in the ground, like those made by the females of many digger wasps. Some wasp nests, such as those of mud daubers and potter wasps, are above ground, constructed of mud cavities attached to twigs, rocks, or human structures. The simplest mud nests contain only one or a few larval cells and are not used by the adults. Other mud nests contain many cells arranged side by side. Among the most intricate nests are those made of paper fibers collected from dry wood and bark and mixed with the wasps' saliva. The vespoid wasps (yellow jackets, hornets, and paper wasps) build nests of this type. In each paper-fiber nest there are one or more combs, or densely packed arrays of larval cells. The adults may congregate on the combs, and some nests have an outer cover, forming a protective refuge for the whole colony.