The term wasp is typically defined as any insect of the order Hymenoptera and suborder Apocrita that is neither a bee nor ant. Almost every pest insect species has at least one wasp species that preys upon it or parasitizes it, making wasps critically important in natural control of their numbers, or natural biocontrol. Parasitic wasps are increasingly used in agricultural pest control as they prey mostly on pest insects and have little impact on crops.
The various species of wasps fall into one of two main categories: solitary wasps and social wasps. Adult solitary live and operate alone, and most do not construct nests; all adult solitary wasps are fertile. By contrast, social wasps exist in colonies numbering up to several thousand strong and build nests—but in some cases not all of the colony can reproduce. In the more advanced species, just the wasp queen and male wasps can mate, whilst the majority of the colony is made up of sterile female workers.
The type of nest produced by wasps can depend on the species and location. Many social wasps produce paper pulp nests on trees, in attics, holes in the ground or other such sheltered areas with access to the outdoors. By contrast solitary wasps are generally parasitic or predatory and only the latter build nests at all. Unlike honey bees, wasps have no wax producing glands. Many instead create a paper-like substance primarily from wood pulp. Wood fibers are gathered locally from weathered wood, softened by chewing and mixing with saliva. The pulp is then used to make combs with cells for brood rearing. More commonly, nests are simply burrows excavated in a substrate (usually the soil, but also plant stems), or, if constructed, they are constructed from mud.