Dermacentor variabilis, also known as the American og tick or wood tick, is a species of tick that is known to carry bacteria responsible for several diseases in humans, including Rocky Mountain spotted fever and tularemia (Francisella tularensis). It is one of the most well-known of hard ticks. D. variabilis does not cause Lyme disease, which is caused by Borrelia burgdorferi carried by the deer tick Ixodes scapularis.