Black Legged Tick “Deer Tick”

Ixodes scapularis

Photo by CDC: Adult Female Black Legged Tick or “Deer Tick”

This hard tick (also known as the “Deer Tick”) is not known to be endemic within Colorado, but has been documented here on dogs that have recently traveled from other states. It is widely distributed, documented in nearly 50% of US counties, with high prevalence in the northeastern and upper Midwestern United States. It is the primary vector of Lyme disease in the US. Commonly co-infected with multiple pathogens this tick also transmits Anaplasmosis, Babesiosis, Powassan Virus disease, Tularemia, Bartonella, and Ehrlichiosis. The bite of this tick may also cause potentially fatal host paralysis via toxins in their saliva. Both its range and prevalence have been expanding throughout the US in recent years. The greatest risk of being bitten exists in the spring, summer, and fall, however adults may be out searching for a host at any time of year. Hosts for this species at the immature stage include a variety of small mammals (notably the white-footed mouse) squirrels, as well as birds. Adult ticks often take their last blood meal on larger mammal hosts, (notably white-tailed deer) where they also breed. Stages most likely to bite humans are nymphs and adult females. Travelers to parts of the country where this tick is prevalent should be vigilant. Many people that are bitten by this tick do not recall the bite due to their small size (as small as a poppy seed) at the nymph stage. It is a common human biter.

Visit University of Rhode Island’s TickEncounter Resource Center for additional photos to help in the identification of ticks.

CDC Distribution Map 2019: This map provides general insight into the expected distribution of these human-biting ticks in the contiguous United States. Populations of ticks may be found outside noted areas. Naturally occurring populations of the Black Legged Tick are not known to occur in Alaska or Hawaii.