By Ann Falk
Geographic Range
Historically, this species was found in most of the eastern United States. It was known from New Hampshire south and west to Pennsylvania and New Jersey, throughout the Appalachians, all of southeast down to the panhandle of Florida, west to eastern Texas, Oklahoma, Kansas and extreme southeastern Nebraska. Populations have also been found along the Mississippi drainage as far north as Minnesota, and in the Ohio River valley throughout southern Illinois and Indiana and extreme southern Ohio. This is the historic extent of the range, but the species has been extirpated in many areas, and populations are patchy and fragmented. (Conant and Collins, 1998)
Habitat
In the northern parts of their range, timber rattlesnakes live in forested rocky hills. In the southern parts of their range these snakes are found in uninhabited swampy areas. Crevices in rocky cliffs usually facing south or large boulders piled together make up the hibernating dens. (Brown, 1993)
These animals are found in the following types of habitat:
temperate 
; terrestrial .
Physical Description
(17.6 to 35.2 oz; avg. 26.4 oz)
(35.43 to 59.84 in)
Adult timber rattlesnakes range from 36-60 inches (90-152 cm) in length, and the record length for the species is 74.5 in. (189.2 cm). They exhibit sexual dimorphism; the males are larger, weighing around 2.0 lb. while the females weigh on an average 1.3 lb. There are several color morphs. The background color of the black morph is gray and the patterns are a rich, velvety black. The background color of the yellow morph is tan, the patterns are a sulfur yellow tinged brownish in patches. Western and southern populations have combinations of these two as well. All the snakes have transverse bands of color. The bands vary geographically; eastern, western, and southern types of timber rattlesnake are recognized. (Brown, 1993, Conant & Collins 1998) (Conant and Collins, 1998; Ernst and Ernst, 2003)
Some key physical features:
ectothermic ; heterothermic ; bilateral symmetry .
Sexual dimorphism: male larger.
Reproduction
Females reproduce every 2 to 6 years, most often they mate every 3 years.
Most breeding activity occurs from mid July to October.
Males follow scent trails to find reproductively active females. Once a male finds a receptive female, he rubs the female's neck with his chin and places his body along hers. The male then rapidly jerks his head and body until he can move his cloaca under hers and insert his hemipenis. Copulation may last for several hours. Males may fight for access to a receptive female. (Ernst and Ernst, 2003)
Mating systems:
polygynous .
Most mating occurs in the summer months, from mid-July to October. Females store sperm through the winter for use in the spring when they emerge from hibernation. Females begin the formation of eggs and yolk in the late summer and fall, those eggs then ovulate the following spring. The live young are born in the autumn, from August through October. Timber rattlesnakes are ovoviviparous, meaning that the eggs are incubated and hatched within the female and she gives birth to live, precocial young. Females give birth to 1 to 20 young, usually 6 to 10 (mean of 10.4). Litter size depends on the size of the female, with larger females having more young. Young are 19.5 to 38.3 cm long (mean 32.5), and weigh from 11.2 to 29.1 grams (mean 22.5). The young have similar patterns to adults, but tend to have a grayish hue. They have their first shedding at 7 to 10 days old, at which point they expose a button-like terminal scale where their rattle will eventually grow. Evn newborn young are dangerous, with fangs from 2.6 to 3.8 mm long and a supply of venom. (Ernst and Ernst, 2003)
Males become sexually mature at 4 to 6 years old; females mature at 7 to 13 years old. Males are mature at snout to vent lengths of 90 to 100 cm. Females are mature at snout to vent lengths of over 100 cm in C. h. atricaudatus and 67 to 90 cm in C. h. horridus. (Ernst and Ernst, 2003)
Key reproductive features:
iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; ovoviviparous .
Female timber rattlesnakes invest significantly in pre-parturition nutrients and protection of their young. They give birth in birthing rookeries, which are often the same sites as winter hibernacula, and stay with the young for 7 to 10 days after birth. At that point the young disperse and become independent. (Ernst and Ernst, 2003)
Parental investment:
pre-fertilization (provisioning, protecting: female); pre-hatching/birth (provisioning: female, protecting: female).
Lifespan/Longevity
[External Source: Max Planck Institute for Demographic Research]
Wild timber rattlesnakes can live over 30 years. Captives have lived 37 years. (Ernst and Ernst, 2003)
Behavior
In the warmer months, timber rattlesnakes are lone predators. During the summer, the snakes are migratory. They roam several miles from their winter den and do not have a permanent home. They cannot tolerate winter and hibernate for up to 7 months each year, returning to the same den each year. They hibernate in dens which are often in rock crevices. These dens may accommodate 15-60 snakes.
The attack stance of rattlers is well-known. The snakes rise vertically with their head and neck forming an S, and when ready they thrust with fangs exposed. Another common behavior of rattlers is ritualized fighting among the males. It often occurs in the periods just before mating season. They lift their bodies and wrap themselves around each other, moving back and forth in a swaying motion, trying to pin each other down. (Brown, 1993)
Key behaviors:
terricolous; motile ; hibernation ; solitary .
Communication and Perception
Like the other snakes in the family Viperidae, timber rattlers are pit vipers. This means they have heat sensitive pit organs located between the nostrils and the eyes. They are sensitive to radiant energy and can distinguish very slight changes in temperature. (Ernst and Ernst, 2003)
Perception channels:
visual ; infrared/heat ; tactile ; vibrations ; chemical .
Food Habits
Their main food source is small mammals, in particular mice, rats, squirrels, and rabbits. Birds are also sometimes killed. The prey is killed when bitten because the snake injects venom. Timber rattlesnakes wait until the animal is dead then swallows prey whole. (Ernst and Ernst, 2003)
Primary Diet:
carnivore (eats terrestrial vertebrates).
Animal Foods:
birds; mammals.
Economic Importance for Humans: Negative
The timber rattlesnake is venomous and can harm humans if they are bitten. However, they typically only bite in defense.
Ways that these animals might be a problem for humans:
injures humans (venomous ).
Economic Importance for Humans: Positive
Timber rattlesnakes play an important part of many ecosystems by keeping the populations of small mammals in check.
Ways that people benefit from these animals:
controls pest population.
Conservation Status
IUCN Red List: [link]:
Least Concern.
US Federal List: [link]:
No special status.
CITES: [link]:
No special status.
Populations of timber snakes are rapidly being depleted across the species' range. The main causes are habitat destruction, snake hunting, and commercial collection for the pet trade. Several states have passed laws protecting the timber snake, but it is not on the threatened species list in many states. The species is not in serious danger but is headed in that direction unless efforts are made to protect it. (Brown, 1993)
Other Comments
While timber rattlesnakes are not aggressive and vicious, their venom is extremely strong. (Grzimek, 1975)
For More Information
Find Crotalus horridus information at
Contributors
Ann Falk (author), University of Michigan.
Tanya Dewey (editor), Animal Diversity Web, University of Michigan Museum of Zoology.
