Parasites exist in huge variety and include animals, plants, and micro-organisms. They may live as ectoparasites on the surface of the host (e.g. arthropods such as ticks, mites, lice, fleas, and many insects infesting plants) or as endoparasites in the gut or tissues (e.g. many kinds of worm), and cause varying degrees of damage or disease to the host
mid 16th century: via Latin from Greek parasitos '(person) eating at another's table', from para- 'alongside' + sitos 'food'