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black-legged or deer tick

black-legged or deer tick (Ixodes scapularis) [female]
Photo © James Gathany

Features and Behaviors

Ticks have four pairs of legs (total of eight legs) in their adult form. The larval form of a tick has six legs. The black-legged or deer tick adult is about 1/8-inch long. The body is red and teardrop-shaped.

There are two populations of deer ticks in Illinois. The larvae of these ticks in the northern one-half of the state feed on mice and other small mammals and can carry Lyme disease. The larvae in the southern part of the state feed on lizards and birds and do not seem to transmit Lyme disease. Larvae molt into pinhead-sized nymphs that feed on mice, larger warm-blooded animals and people. In the fall, they molt into adults that feed mainly on white-tailed deer (Odocoileus virginianus). Female deer ticks lay eggs the following spring. The deer tick has been found in many Illinois counties, but in recent years it has been common only in specific areas, mostly in northern Illinois. This species can transmit Lyme disease as well as babesiosis and anaplasmosis. Local health departments and the Illinois Department of Public Health (217-782-2016 or can provide more information about ticks and the diseases that they can carry.

Illinois Range


​Kingdom: Animalia
Phylum: Arthropoda
Class: Arachnida
Order: Ixodida
Family: Ixodidae

Illinois Status: common, native