An organism that lives on or in another organism (its host). Parasites exist in a huge variety, including animals, plants, and microorganisms. Ectoparasites live on the surface of the host (e.g., ticks, mites, lice, fleas, and many insects infesting plants). Endoparasites live in the gut or tissues (e.g., many kinds of worm), and cause varying degrees of damage or disease to the host. Parasite comes from the Greek words parasitos (eating at another's table), which is composed of para (alongside) and sitos (food).