any one wasp of the subfamilies Eumenii-nae, Euparagiinae, and Zethinae of the family Vespidae. There are more than 2,000 species of solitary wasps. The female builds a nest with one or more cells; an egg is laid in each cell. The larvae are fed dead caterpillars, beetle larvae, and sawfly larvae. Most commonly the food is placed alongside the larvae (Eumenes, potter wasps). The female of some species directly feeds the larvae pieces of insects. Solitary wasps are beneficial, because they reduce the number of harmful insects.