General Description: The Prairie Rattlesnake is South Dakota’s only species of venomous snake. Prairie Rattlesnakes are a large, heavy-bodied species of snake, with adults ranging from 36–50 inches (91.4–127.0 cm) in length. The background coloration is light gray, tan, or light brown with pronounced dorsal dark brown blotches ringed in white running the length of the body. These blotches of fade towards the tail and turn into bands. Smaller, often lighter, blotches run along the sides. Two white lines occur on each side of the face: one runs between the eye and the nostril and along the upper lip and the other begins behind the eye and runs down the neck. Prairie Rattlesnakes have elliptical pupils and a single heat pit located between the eye and the nostril that allows individuals to use thermal detection of prey and predators. The belly is off-white or light yellow and unmarked. Scales on this species are heavily keeled, giving individuals a rough texture, and the anal scale is not divided. Juvenile coloration is similar to adult coloration. Many large non-venomous snakes are confused with the Prairie Rattlesnake because they often vibrate their tail (that makes a rattlesnake-like noise when it hits dry leaves or sticks), however, Prairie Rattlesnakes have a true rattle on the end of their tails. This rattle is remarkably energetically efficient and is made of keratin. Rattlesnakes are born with a “button” and are unable to make noise with their rattle until they have their first shed. Contrary to popular belief, you cannot age a rattlesnake by counting the number of segments on the rattle. Rattlesnakes gain segments every time they shed their skin, which can be multiple times per year (depending on how much they grow). These keratinized rattles also get brittle, crack, and break off.
Behavior: Prairie Rattlesnakes feed primarily on rodents, but will also consume birds and lizards. These are ambush predators and will wait until prey move within striking distance before envenomating prey with hemotoxic (tissue degrading) venom. As with all other rattlesnakes, Prairie Rattlesnakes have two large, hinged fangs that are folded at the top of the mouth when at rest. It is commonly believed that juvenile rattlesnakes are more dangerous than adults due to their perceived inability to control the amount of venom that they inject, however, there is no evidence to support these claims. Prairie Rattlesnakes have cryptic coloration that can make them difficult to locate when they are not moving. As such, their first line of defense is their camouflage coloration. However, when disturbed, Prairie Rattlesnakes will rattle their tail and will strike if continued to be provoked. Individuals will often den in the same hibernacula every winter and densities when denning can be quite high.
Reproduction: Mating often takes place in late spring and early summer after individuals have emerged from hibernation. Males will compete in combat rituals where individuals will intertwine with one another attempting to push the other down to the ground, with the winner having access to mate with a nearby female. Females give birth to 8–17 live young and will remain with juveniles for several days after being born and exhibit maternal parental care.
Habitat: Prairie Rattlesnakes can be found in grasslands, prairies, alpine meadows, and spruce forests throughout their range where they are often associated with rocky outcrops or prairie dog towns, which provide cover and are where individuals overwinter.
Species Range: This species can be found throughout the western Great Plains and the Rocky Mountains from west Texas north to southern Canada. An isolated population in the Loess Hills of northwest Iowa represents the easternmost population of this species.
South Dakota Range: Prairie Rattlesnakes are abundant and frequently encountered throughout western South Dakota (west of the Missouri River). Few isolated records of individuals also occur along the Missouri River in southeastern South Dakota, but likely represent translocated individuals rather than established populations.
South Dakota Status: This species is not listed by the South Dakota Game, Fish and Parks.
Account written by Drew R. Davis and Jessica E. Romero