A wasp is any insect of the order Hymenoptera and suborder Apocrita that is neither a bee nor an ant. This means that wasps are paraphyletic with respect to bees and ants, and that all three groups are descended from a common ancestor; the Apocrita form a clade.
The most commonly known wasps such as yellow jackets and hornets are in the family Vespidae and are eusocial, living together in a nest with an egg-laying queen and non-reproducing workers. Eusociality is favoured by the unusual haplodiploid system of sex determination in Hymenoptera, as it makes sisters exceptionally closely related to each other. However, the majority of wasp species are solitary, with each adult female living and breeding independently. Many of the solitary wasps are parasitoidal, meaning that they raise their young by laying eggs on or in the larvae of other insects. The wasp larvae eat the host larvae, eventually killing them. Solitary wasps parasitize almost every pest insect, making wasps valuable in horticulture for biological pest control of species such as whitefly in tomatoes and other crops.