The common name blacklegged refers to their dark legs which are in contrast to the paler body and that of deer because the preferred adult host is the white-tailed deer; in the mid-west, it is called the bear tick. This tick is of medical importance because it is an important vector of Lyme disease. Blacklegged ticks are found primarily in the northeastern, midwestern, and southeastern states in the United States, but extend into Mexico.
Lyme disease is caused by the spirochete, Borrelia burgdorferi Johnson, Schmid, Hyde, Steigerwalt & Brenner, which is a corkscrew-shaped bacteria. Its primary wild reservoir is the white-footed mouse which is infected by the spring-feeding, pathogen-infected blacklegged/deer tick nymphs. These white-footed mice then serve to infest the later-feeding blacklegged/deer tick larvae, which keeps the disease cycle going. Tick eggs don’t contain the spirochete, so it is acquired via feeding.
A favorite feeding area for these ticks on humans is at the back of the neck, at the base of the skull; long hair makes detection more difficult.