Otobius megnini, which is exceedingly specialized biologically and structurally, infests the ear canals of pronghorn antelope, mountain sheep, and Virginia and mule deer in low rainfall biotopes of western USA and in Mexico and western Canada. Cattle, horses, goats, sheep, dogs, and people are similarly infested. This well-concealed parasite has been transported with livestock to western South America, Galapagos, Cuba, Hawaii, India, Madagascar, and southeastern Africa. Notably, adults have nonfunctional mouthparts and remain nonfeeding on the ground but may survive for almost 2 yr. Females can deposit as many as 1,500 eggs in a 2-wk period. Larvae and two nymphal instars feed for 2–4 mo, mostly in winter and spring. There can be two or more generations per year. In contrast with most other ticks, the bites of O megnini are painful for the hosts. People and other animals may suffer severe irritation from ear canal infestations, and heavily infested livestock lose condition during winter. Tick paralysis of hosts and secondary infections by larval screwworms are reported. O megnini is infected by the agents of coxiellosis/Q fever, tularemia, Colorado tick fever, and Rocky Mountain spotted fever, although its ability to transmit these pathogens to the hosts is uncertain. The second Otobius sp, O lagophilus, feeds on the heads of jackrabbits (hares) and rabbits in western USA.