The Black-Legged Tick is a three-host tick, each individual feeds three times on three different host animals. Host animals include, but are not limited to, lizards, birds, white-footed mice, dogs, cats, horses, cows, opossums, foxes, raccoons, white-tailed deer, humans and other small mammals. Each active stage of the tick larva, nymph and adult feeds only once and feeds slowly, requiring several days to a week to take in the blood meal. Two years are required for the black-legged tick to complete its life cycle.

Engorged females lay their eggs on the ground in the spring and these hatch into larvae later in the summer. August is the first month of peak larval activity. Larvae feed for a week or less, drop from host animal and molt to nymphs. Nymphs appear the following year in late spring and summer. June is the month of peak nymphal activity. Nymphs feed for approximately a week, drop to the ground and appear as adults in the fall. September is the month of peak adult activity.

The black-legged tick, Ixodes Scapularis (also commonly now as the deer tick, I .Dammini) and the western black-legged tick, I. Pacificus are the principal vectors of Lyme disease caused by the spirochete, Borrelia Burgdorferi. Since surveillance for Lyme disease begun by the Center for Disease and Prevention (CDC) in 1982, the number of humans cases has increased from 491 to 16,461 in 1996. Lyme disease occurs mainly in the northeastern, mid-Atlantic and the north central states, and in California. New York, Connecticut, Pennsylvania, New Jersey, Rhode Island and Massachusetts account for over 76% of the reported cases.

Lyme disease often begins in humans with expanding skin lesions, erythema migraine accompanied by malaise, fatigue, chills, fever, headache or stiff neck. A year or more after the tick bite, symptoms of persistent infection may include numbness or tingling of the extremities, disturbance in memory, mood or sleep and chronic arthritis (typically the large joins, especially the knees).