Dermacentor variabilis

Wood or Dog Tick

The wood tick (also called the American dog tick) is the most commonly encountered tick in the Upper Midwest, and is also common throughout the eastern and southern United States and some parts of the west coast.  

Every county in the Midwest has this tick, which is active from late March through August. The tick’s life cycle may be completed in one or two years in this region.  For a tick, the female American dog tick is large, with a patterned, cream-colored shield covering the front portion of the body.  The male is usually smaller, with a cream-colored shield that covers almost the entire upper body. Both are usually a chocolate brown color. Larvae and nymphs usually feed on small mammals, especially rodents. Adult ticks most often feed on dogs and other large mammals, including humans.

American dog ticks are carriers of the bacteria Rickettsia rickettsii that cause Rocky Mountain spotted fever, or RMSF.  This disease is rare across the Midwest.  In Iowa, for example, only 106 cases were reported from 1990 to 2014. 

Dog ticks can also can transmit the bacteria Francisella tularensis that cause tularemia, or rabbit fever.  In addition, they may cause tick paralysis, an uncommon but potentially fatal malady in which a female tick that has been attached for days paralyzes its host, though the paralysis disappears within a few hours of the tick’s removal.

Videos of questing dog ticks

To find a host from which to take a blood meal, tick larvae, nymphs, and adults climb leaves and sticks, extend their front legs, and wait for potential hosts to come by. Heat, movement, and other signals like carbon dioxide given off by host animals cause the ticks to move quickly onto the passing host. These amazing videos by Dr. Graham Hickling at the University of Tennessee Center for Wildlife Health show questing dog ticks. The videos show adults of both sexes.