Usefulness is a subjective term, but wasps, which with bees and ants make up the order Hymenoptera, are extraordinarily well adapted to certain human ends.
Almost all are predators or parasites of injurious pests, and some act as pollinators of valuable plants.
With varying degrees of success, wasps of different species have been bred, imported or encouraged to fight these problems:
Corn ear worms and tobacco bud worms, which attack at least one hundred plants, including corn, cotton, soybeans and tomatoes; the eucalyptus longhorn borer beetle; the alfalfa weevil; flies plaguing tourists on Mackinac Island, Michigan; the gypsy moth; tomato hornworms; hemlock scales; wood-boring insects; and the Colorado potato beetle.
Other wasp species fight Mexican bean beetle larvae, which attack snap and lima beans and soybeans, and the cereal leaf beetle, attacking wheat, oats and barley.
Fig trees and several species of the ornamental ficus tree also depend on specific wasp species for pollination.