Description: Adults usually grow to total length of 36–60 inches. In Pennsylvania, the smallest size females that could produce viable eggs was 28.4 inches. Most adult timber rattlesnakes found measure less than 45 inches in total length and weigh between 1.1 and 3.3 lbs., often being towards the lower end of that range. The maximum reported total length is 74.5 inches.
The dorsal scales are keeled and arranged in 21–26 scale rows at midbody (usually 25 rows in the southern part of its geographic range, and 23 rows in the northern part). The ventral scales number 158–177 in males and 163–183 in females. Males have 20–30 subcaudal scales, while females have 15–26. The rostral scale is normally a little higher than it is wide. In the internasal-prefrontal area there are 4–22 scales that include 2 large, triangular internasal scales that border the rostral, followed by two large, quadrangular prefrontal scales (anterior canthals) that may contact each other along the midline, or may be separated by many small scales. Between the supraocular and internasal scales, only a single canthal scale is present. Five to seven intersupraocular scales are seen. The number of prefoveal scales varies between two and eight. Usually, the first supralabial scale is in broad contact with the prenasal scale, although slightly to moderately separated along its posteroventral margin by the most anterior prefoveals.
Dorsally, they have a pattern of dark brown or black crossbands on a yellowish-brown or grayish background. The crossbands have irregular zig-zag edges, and may be V- or M-shaped. Often a rust-colored vertebral stripe is present. Ventrally, they are yellowish, uniform, or marked with black. Melanism is common, and some individuals are very dark, almost solid black.
Habitat: Generally, this species is found in deciduous forests in rugged terrain. During the summer, gravid (pregnant) females seem to prefer open, rocky ledges where the temperatures are higher, while males and nongravid females tend to spend more time in cooler, denser woodland with more closed forest canopy.
Range: This species ranges widely in the United States, ranging marginally into southern Canada (where it is extinct). Its range extends from central New England to northern Florida, and west to eastern Texas, central Oklahoma, eastern Kansas, southeastern Nebraska, southern and eastern Iowa, and southeastern Minnesota. The distribution is spotty along the western and northern edges of the range. Sizeable populations still occur in the Appalachian Mountains from Pennsylvania though the Virginias, across eastern Kentucky and Tennessee to northeastern Alabama, in the Ouachita and Boston mountains of Arkansas and extreme eastern Oklahoma, in heavily wooded sections of the southeastern Coastal Plain from North Carolina to northeastern Florida and west to Louisiana and southern Arkansas, and in the Piedmont in the Uwharrie National Forest of central North Carolina and Pine Mountain of west-central Georgia. Dens occur at elevations of up to about 5,000 feet in the southern Appalachians, 2,200 feet in southern New England, and about 1,300 ft in northeastern New York, Wisconsin, and Minnesota; individuals may range to higher elevations in summer.
Venom: Potentially, this is one of North America's most dangerous snakes, due to its long fangs, impressive size, and high venom yield. Considerable geographic and ontogenetic variation occurs regarding the toxicity of the venom, which can be said for many rattlesnake species. Four venom patterns have been described for this species: Type A is largely neurotoxic, and is found in various parts of the southern range. One effect of the toxin can be generalized myokymia. Type B is hemorrhagic and proteolytic, and is found consistently in the north and in parts of the southeast. Type A + B is found in areas where the aforementioned types apparently intergrade in southwestern Arkansas and northern Louisiana. Type C venom has none of the above components and is relatively weak.
The neurotoxic component of the type A venom is referred to as canebrake toxin, and is a phospholipase A2. It is analogous to the neurotoxins found in the venoms of several other rattlesnake species, and when present, contributes significantly to the overall toxicity. Other components found in the venom include a small basic peptide that works as a myotoxin, a fibrinogen-clotting enzyme that can produce defibrination syndrome, and a bradykinin-releasing enzyme.
CroFab antivenom, while not specific for C. horridus, is used to treat envenomations from this species.
Diet: Their prey are mainly small mammals, but may include small birds, frogs, and other small animals, including other snakes. Although capable of consuming other rattlesnakes, the most common snake they prey upon are garter snakes. Like most rattlesnakes, timber rattlesnakes are known to use chemical cues to find sites to ambush their prey and often strike their prey and track them until they can be consumed. Timber rattlesnakes are known to use fallen logs as a waiting site for prey to pass by, giving them an elevated perch from which to effectively strike their prey, which is almost entirely terrestrial rather than arboreal (even arboreal prey such as squirrels tend to be caught when they come to the ground). If the arboreal prey (squirrels) are in the trees, it was found that the snake might indicate vertical tree posture, meaning it leans up against a tree looking at the squirrel and waiting for it to come down.
Reproduction: Females mature at about 5 years old and reproduce every two to three years. Mating season takes place from spring to late summer. Males compete for females and display a courtship "dance." The dance has three steps; the male first slides next to the female, then rubs his head and body against her, and finally curls his tail under her tail to mate. Pregnant, or gravid, females move into more open habitat while males stay in habitats with more tree cover.
Timber rattlesnakes are viviparous, meaning they give birth to live young. A single litter can have three to 13 snakes. Young rattlesnakes resemble adults, except that they have only one button on their tail and may have a stripe from their eyes to their jaws. As they grow, the young snakes molt their skin creating room to grow additional rattles. Larger timber rattlesnakes may have up to five or six rattles and may shed a button as new buttons grow.
Status: Listed as Least Concern in view of its very wide distribution, presumed large population, and because it is unlikely to be declining fast enough to qualify for listing in a more threatened category. The timber rattlesnake is listed as endangered in New Jersey, Ohio, Vermont, Connecticut, Massachusetts, Virginia, Indiana, New York, Illinois, and New Hampshire. Timber rattlesnakes have already been extirpated in Maine and Rhode Island and only one population remains in New Hampshire. They are protected in many of the Appalachian states, but their populations continue to decline.
Disclaimer: ITIS taxonomy is based on the latest scientific consensus available, and is provided as a general reference source for interested parties. However, it is not a legal authority for statutory or regulatory purposes. While every effort has been made to provide the most reliable and up-to-date information available, ultimate legal requirements with respect to species are contained in provisions of treaties to which the United States is a party, wildlife statutes, regulations, and any applicable notices that have been published in the Federal Register. For further information on U.S. legal requirements with respect to protected taxa, please contact the U.S. Fish and Wildlife Service.
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