Parasites (Topical Term)

The Amer. Herit. dict. of the Engl. lang., via WWW, Mar. 20, 2002 (parasite: 1. Biology An organism that grows, feeds, and is sheltered on or in a different organism while contributing nothing to the survival of its host)

OED online, Mar. 20, 2002 (parasite: 2. a. Biol. An animal or plant which lives in or upon another organism (technically called its host) and draws its nutriment directly from it. Also extended to animals or plants that live as tenants of others, but not at their expense (strictly called commensal or symbiotic); also to those which depend on others in various ways for sustenance, as the cuckoo, the skua-gull, etc.; and (inaccurately) to plants which grow upon others, deriving support but not nourishment from them (epiphytes), or which live on decaying organic matter (saprophytes).)