There are approximately 900 species of ticks worldwide, with 20 species occuring in Illinois.
The 4 species that people in Illinois are likely to encounter are the American Dog tick, Black-legged tick, Lone Star tick, and Brown Dog tick.
American Dog Ticks, (Dermacentor variabilis) are the most commonly encountered in Illinois. Adults are active from April to September and can carry the pathogens for Rocky Mountain Spotted Fever and Tularemia.
The Black-legged Tick (Ixodes scapularis) is present year round and can carry the pathogens for Lyme disease, Babesiosis, and Anaplasmosis. All life stages of the Black-legged Tick will bite humans. This tick is also called Deer Tick.
The Lone Star Tick (Amblyomma americanum) is found from April through fall and all stages will bite humans. The Lone Star Tick can carry the pathogens for Rocky Mountain Spotted Fever, Tularemia, and Erlichiosis.
The Brown dog tick (Rhipicephalus sanguineus) rarely bites humans and is not an important carrier of diseases for humans. This tick is a tropical species and unable to survive outdoors during Illinois winters.