Timber Rattlesnake Crotalus horridus - Endangered

Adult male from Brown County

Identification

Adult Timber Rattlesnakes are among the most distinctive snakes in Indiana as they are incredibly large and heavy-bodied with strongly keeled scales and a segmented keratinous rattle at the tip of the tail. Contrary to popular belief, the snakes are hesitant to use this rattle and prefer to remain hidden, when possible. In fact, snakes typically only rattle at people if they are moving over open ground when approached or are physically touched. Importantly, many other snakes will vibrate their tails when threatened, thus making an audible rattle sound. Hearing a snake rattle its tail is not sufficient to identify it as a rattlesnake, though seeing the physical rattle is. Juvenile Timber Rattlesnakes may have only a single "button" on their tail tip and are incapable of making a sound, but adults may have long, tapered rattles of 15 segments or more. Though a rattlesnake's rattle length is indicative of age, most older snakes have broken rattles. Timber Rattlesnakes are otherwise unique in that their coloration transitions from very light near the head and neck, and darkens posteriorly, ending in a velvety black tail. Though many snakes are brown or gray in color, bright yellow-gold rattlesnakes are common in Indiana. Black chevrons run from the neck down the back with a light orange-brown vertebral stripe down the middle. Timber Rattlesnakes are not the longest snake in the state, but they are, undoubtedly, the heaviest as large males are often more robust than a man's forearm. Adult females are typically two to three feet (60 - 90 cm) in length, but adult males commonly exceed four feet (1,2 m) with some individuals growing to nearly five feet (1.5 m) in length.

Adult female from Brown County
Combatting males from Monroe County

Adult Timber Rattlesnakes are so heavy bodied and distinctive, that they are difficult to mistake for any other native species. Eastern Hog-Nosed Snakes are perhaps the most similar species in Indiana as they are also robust for their size and exhibit a similar range of color variants (dark gray-brown to yellow-orange). However, Eastern Hog-Nosed Snakes have a blotched dorsal pattern, instead of a chevron pattern, have a distinctly upturned snout, and lack a rattle. Juvenile Timber Rattlesnakes are light gray in color and are similar to juvenile Eastern Copperheads, but have chevrons instead of hour-glass bands and have a small button at the tip of the tail, where copperheads have a light yellow-green tail tip.

All four of Indiana's venomous snakes have thick bodies, broad chunky heads, elliptical pupils, heat sensitive pits between the eyes and nostrils, and undivided post-anal ventral scales (under the tail). However, most of these characteristics require close examination, elliptical pupils can dilate and become round, and many non-venomous snakes (especially Eastern Hog-Nosed Snakes) will broaden and flatten their heads in self-defense. Therefore, it is always best to treat any snake that you cannot positively identify as potentially venomous. Venomous snakes are best left alone as most snake bites occur when someone attempts to handle or kill the snake. Snakes are not aggressive and do not hunt, attack, or chase people when left unmolested.

Ecology and Conservation

Timber Rattlesnakes are generally associated with eastern deciduous or mixed deciduous/coniferous forest in rugged terrain. In southcentral Indiana, where much of the Midwest research on Timber Rattlesnakes has taken place, timbers occur in large tracts of well-developed oak hickory forest in steeply dissected ridge/valley terrain. Habitat preference of the Timber Rattlesnake is highly influenced by reproductive condition. Age class also appears to be a factor in Timber Rattlesnake habitat selection. Juvenile timbers prefer areas with more complete canopy closure than adult snakes and often associate with structures offering cover such as logs, shrubs, or woody debris. The Timber Rattlesnake is highly dependent on the existence of suitable winter denning habitat. Absence of suitable den sites is likely a chief determinant of the historical range of the Timber Rattlesnake. Timber Rattlesnakes, like all rattlesnakes, do not lay eggs but give birth to “live” young. They are sit-and-wait predators that rely on motionlessness and cryptic coloration to ambush prey and feed primarily on small mammals.

Unglaciated forest in Brown County
Mesic forest in Brown County

Because of low reproductive output, Timber Rattlesnake populations are extremely fragile and susceptible to degradation by human activities. Of particular concern is the protection of den sites, which are often rare or widely dispersed across the landscape. Collecting and deliberate killing of Timber Rattlesnakes is also a chief threat. Although not federally listed as Threatened, the Timber Rattlesnake is recognized as imperiled throughout the Midwest. It is listed as Endangered by the states of Indiana and Ohio, and Threatened in Illinois and Minnesota. They are highly susceptible to road mortality and have also been the victim of targeted persecution for many years. A combination of direct persecution and habitat loss/fragmentation are to blame for the dramatic decline of this iconic snake in Indiana. They are now protected in Indiana, as a state endangered species.

Distribution

Once found throughout much of southern Indiana, Timber Rattlesnakes are now restricted, predominantly, to the rugged forests of Brown County and portions of adjacent Morgan and Monroe Counties. A small population also remains in Jackson and Washington Counties and snakes are periodically reported from Perry County, though the status of these remnant populations is largely unknown. Timber Rattlesnakes are large, slow-moving snakes and males may range across more than 200 acres (100 hectares) during the breeding season.

Taxonomy

Scientists debate whether to recognize subspecies of the Timber Rattlesnake (Crotalus horridus). For those that subscribe to this subspecific taxonomy, Indiana is home to the Timber Rattlesnake (C. h. horridus). These snakes are members of the family Viperidae, which is represented by a total of four species in Indiana.

Literature Cited

Conant, R. and J. T . Collins. 1998. Reptiles and Amphibians of Eastern and Central North America. Third Edition, Expanded. Houghton Mifflin, New York, NY.

Minton, S. A. Jr. 2001. Amphibians and Reptiles of Indiana. Indiana Academy of Science, Indianapolis, IN.

Distribution Map
Distribution map of Timber Rattlesnake (Crotalus horridus)
Photographs