By far the greater number of wasp species (over 100,000) are the parasitic wasps. Most of them are parasitoids which lay their eggs in the caterpillars of other insect species. Almost every pest insect species has at least one wasp species that preys upon it or parasitizes it. This makes wasps vital to the natural control of pest numbers (biocontrol). Parasitic wasps are increasingly used in agricultural pest control as they prey mostly on pest insects and have little impact on crops.