The great majority of wasps are solitary wasps; they live alone. All the females are fertile. A typical female solitary wasp lays her eggs in, on, or next to an insect or spider that she has paralyzed with her venom and placed in her nest. In most species, the nest is either a small structure the female constructs from mud, or a hole the female digs in the ground. Some solitary wasps lay their eggs in the leaves or stems of plants. As a larva develops, it uses the insect, spider, or plant for food. The females of some species guard their nests; those of others abandon them. Males, depending on the species, survive for the summer or die soon after mating. Many solitary wasps survive winter as pupae.

There are many different kinds of solitary wasps. Digger wasps and sand wasps dig underground nests; some of these wasps bring captured prey to their larvae. Potter, or mason, wasps make nests consisting of roundish chambers of mud, usually attached to twigs. Mud daubers make nests consisting of joined tubular cells of mud, usually under eaves. Gall wasps lay their eggs in plant tissue. Ichneumon flies are wasps that lay their eggs in or on larvae of other insects. Velvet ants (wasps that look like hairy ants) and cuckoo wasps lay their eggs in the nests of other wasps or of bees.

Wasps belong to the order Hymenoptera. Yellow jackets, hornets, and paper wasps belong to the family Vespidae. Some biologists also place potter wasps in the family Vespidae; others, in the family Eumenidae. Digger wasps, sand wasps, and mud daubers belong to the family Sphecidae; gall wasps to the family Cynipidae; ichneumon flies to the family Ichneumonidae; velvet ants to the family Mutillidae; cuckoo wasps to the family Chrysididae.