A wasp is any insect of the order Hymenoptera and suborder Apocrita that is neither a bee nor an 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.
In wasps, as in other Hymenoptera, sexes are significantly genetically different. Females have 2n number of chromosomes and come about from fertilized eggs. Males, in contrast, have a haploid (n) number of chromosomes and develop from an unfertilized egg. Wasps store sperm inside their body and control its release for each individual egg as it is laid; if a female wishes to produce a male egg, she simply lays the egg without fertilizing it. Therefore, under most conditions in most species, wasps have complete voluntary control over the sex of their offspring.
Anatomically, there is a great deal of variation between different types of wasp. Like all insects, wasps have a hard exoskeleton covering their three main body parts. These parts are known as the head, mesosoma and metasoma. Wasps also have a constricted region joining the first and second segments of the abdomen (the first segment is part of the mesosoma, the second is part of the metasoma) known as the petiole. Like all insects, wasps have three sets of two legs. In addition to their compound eyes, wasps also have several simple eyes known as ocelli. These are typically arranged in a triangular formation just forward of an area of the head known as the vertex.
It is possible to distinguish between sexes of some wasp species based on the number of divisions on their antennae. For example, male yellowjacket wasps have 13 divisions per antenna, while females have 12. Males can in some cases be differentiated from females by virtue of having an additional visible segment in the metasoma. The difference between sterile female worker wasps and queens also varies between species but generally the queen is noticeably larger than both males and other females.
Wasps can be differentiated from bees, which have a flattened hind basitarsus. Unlike bees, wasps generally lack plumose hairs.