Most Ticks are minute to small (e.g. 0.08–1.00 millimetre or 0.0031–0.039 inch), but the largest Acari (some ticks and red velvet mites) may reach lengths of 10–20 millimetres (0.39–0.79 in). It is estimated that over 50,000 species have been described (as of 1999) and that a million or more species are currently living.

Ticks feed on the blood of mammals and occasionally reptiles. They latch on to their host by cutting in to the top layer of skin and using a natural anticoagulant to stop the bleeding. Ticks bury their head inside the wound and feed on the host.

Ticks have been known to carry Lyme disease, Q fever, Colorado tick fever, tularemia, tick-borne relapsing fever, babesiosis, ehrlichiosis and tick-borne meningoencephalitis, as well as bovine anaplasmosis.