Noun
Any parasite which lives on the exterior of animals; -- opposed to endoparasite.
Source: Webster's dictionaryBeetles and flies dominate Heard Island's known insect fauna, which comprises up to 21 species of ectoparasite (associated with birds and seals) and up to 13 free-living species. Source: Internet
When our ancestors adopted group-dwelling social arrangements roughly 1.8 mya, ectoparasite loads increased dramatically. Source: Internet