limit bacterial infections. It is likely, though little researched, that most parasitic (disease-causing) micro-organisms have hyperparasites which may prove widely useful in both agriculture and medicine. Hyperparasitism is to an extent analogous to predation on herbivores, which in turn eat plants, as there are three trophic levels involved. However, hyperparasites are smaller than predators, breed more rapidly than their hosts and are generally found in larger numbers, while especially in the case of micro-organisms, their hosts can sometimes clear their infection. Hyperparasitism may thus behave differently from three-level predator-prey systems: predators can exert control of prey populations, for instance as keystone species, but given the differences between hyperparasites and predators, their effects may need to be modelled differently. In literature Jonathan Swift refers to hyperparasitism in these lines from his poem "On Poetry: A Rhapsody": See also Hyperparasitoid Notes References Hyperparasites