Definition: An acarine of the families Ixodidae (hard ticks) or Argasidae (soft ticks), which contain many bloodsucking species that are important pests of humans and domestic birds and mammals, and that probably exceed all other arthropods in the number and variety of disease agents that they transmit. Ticks are differentiated from the much smaller true mites by possession of an armed hypostome and a pair of tracheal spiracular openings located behind the basal segment of the third or fourth pair of walking legs; the larva (seed tick) has six legs, and after molting appears as an eight-limbed nymph. Some important ticks are Amblyomma americanum (Lone Star tick) and A. hebraeum (South African bont tick); Argas persicus (adobe, fowl, or Persian tick) and A. reflexus (pigeon tick); Boophilus (cattle ticks); Dermacentor albopictus (horse or winter tick), D. andersoni (Rocky Mountain spotted fever or wood tick), D. nitens (tropic horse tick), D. occidentalis (Pacific or wood tick), and D. variabilis (American dog tick); Haemaphysalis chordeilis (bird tick) and H. laporis-palustris (rabbit tick); Ixodes pacificus (California black-legged tick), I. pilosus (paralysis tick), I. ricinus (castor bean tick), and I. scapularis (black-legged or shoulder tick); Ornithodoros coriaceus (pajaroello tick) and O. moubata (African relapsing fever or tampan tick); and Rhipicephalus everti (African red tick), R. sanguineus (brown dog tick), and R. simus (black-pitted tick).
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