ectoparasitism

Ectoparasitism is a form of parasitism in which the parasite lives on the exterior of its host, deriving resources from the host without residing inside its body. Most ectoparasites are arthropods, including insects such as lice, fleas, bed bugs, and some true bugs, as well as arachnids like ticks and mites. They can be permanent residents, remaining on the host for extended periods, or temporary visitors that feed and then depart. Some species are obligate ectoparasites, spending their entire life cycle on the host, while others are facultative and exploit hosts only for feeding or reproduction.

Ectoparasites attach to the host with specialized mouthparts, claws, or suction structures and typically feed on blood, skin tissue, or secretions. Hematophagy is common and can cause irritation, itching, dermatitis, anemia, and reduced host fitness. Ectoparasites can also act as vectors for pathogens, facilitating the spread of diseases such as Lyme disease and other borrelioses by ticks, plague and typhus by fleas and lice, and scrub typhus by mites. In addition to disease transmission, ectoparasitism can influence host behavior and social interactions, and ecological interactions may shape parasite communities on hosts.

Host defenses include grooming, immune responses, and behavioral adaptations to remove parasites. Ecology and evolution drive host specificity and parasite life cycles, with some species adapted to particular hosts or habitats, including domestic animals, wildlife, and aquaculture systems. Control measures in human and veterinary contexts often combine environmental management, repellents, and targeted pesticides to reduce ectoparasite burdens and disease risk.