The timber rattlesnake averages 36 to 60 inches in length. It has a heat-sensitive pit on each side of the head between the eye and the nostril. Its head is ﬂattened and much wider than the neck. The pupil of each eye is vertically elliptical. A rattle is present at the tip of the tail. The scales are keeled (ridged). The body is gray, yellow or green-white with a series of dark bands along the back. A rust-colored stripe is present in the middle of the back. A dark bar may be found between the eye and jaw.
The timber rattlesnake may be found in those Illinois counties that border the Mississippi River and that have forested river bluffs. It also may be found in the southern one-third of Illinois. This snake lives in forested bluffs, abandoned sawdust piles and rock outcrops and may be found in fields in summer. The timber rattlesnake is active during the day until temperatures become too high in summer. It then becomes nocturnal. Much of the time is spent hiding. The rattle is developed as the skin is shed. A button at the tip of the tail is present at birth. Each time the skin is shed a new segment is added to the rattle. The snake may shed its skin from three to ﬁve times in a year. Counting segments of the rattle is not a good method of aging a snake as the number of segments added each year varies and segments may be broken or lost. When disturbed, it will try to escape or coil and rattle the tip of the tail producing a buzzing noise. It hibernates in dens in rock crevices with other species of snakes. Females reach maturity at the age of four or ﬁve years. Mating occurs in July and August. The female gives birth to from six to 10 young in August, September or October of the following year. Mature females reproduce every other year. This snake injects its prey with venom then waits for it to succumb before eating it. The timber rattlesnake eats rodents and birds but will take frogs and lizards.