Many different varieties of wasps exist, with widely varying habits and structural characteristics. They may be divided into the social wasps and the solitary wasps. Among the former are the hornets, the yellow jackets, and the large, mahogany-colored wasps known as the paper wasps; they live in communities consisting of males, females, and sterile workers. The solitary wasps, including the mud daubers, potter wasps, and digger wasps, produce no workers and build individual nests. Wasps vary greatly in size. Some of the parasitic wasps are so small that several may develop in a small insect egg. Other species attain a body length of about 5 cm (about 2 in). The female and worker wasps have a sting, which is used to attack their prey or to protect them against molesters. Wasp venom contains histamine and a factor that dissolves red blood cells. A wasp sting can be fatal to a sensitive person. Desensitization can be accomplished by injections of antigen extracts.

Although adult wasps are largely carnivorous, some also eat vegetable matter, such as overripe fruit. As a rule, young wasps are fed entirely on other insects or insect remains. Many parasitic varieties, which lay their eggs in the body or egg of the host, are useful in the control of some injurious pests such as aphids, codling moths, and bollworms.

Social wasps build papery nests of masticated fibers. The nests of yellow jackets and hornets are composed of several layers of cells enclosed in a globular outer covering. Paper wasps build open, flat nests of a single comb. The nest is begun by the queen wasp, which alone survives the winter. The first eggs develop into workers, which continue the nest building and largely take over the care of the young. During a season a paper wasp nest may become up to 20 cm (8 in) in diameter and house several hundred wasps. Several thousand yellow jackets may exist in one community.