An organism that lives at the expense of another (its host); impedes its growth and eventually kills it. Insect parasitoids, which are often very tiny, attack a single organism (plant or animal); from which they derive everything they need for their own growth and reproduction. One way a parasitoid does this is by laying its eggs in the body of the host insect. Parasitoids are being used more and more for biological control of insect pests, thus reducing the need for chemical insecticides. Predators, unlike parasitoids, prey on more than one organism and kill and consume their tissues.