- Distribution: counties along the eastern side of the Missouri River and all counties in western South Dakota
- Rattle segment(s) at the end of the tail
- Pits below the midline of each eye and each nostril
- Pupil of the eye is elongate rather than round
- Upper body is light brown to greenish with dark, light-bordered blotches along back
- Triangular-shaped head
- Keeled scales
- Diet: rodents (including mice, ground squirrels, and the young of prairie dogs or cottontails), other snakes, lizards, and birds
- Habitat: open prairies, haylands, and croplands
The rattles and their distinctive rattling sound are the most recognizable feature of this snake. The Prairie Rattlesnake is the only venomous snake native to South Dakota. Young rattlesnakes are born with a prebutton, a rattle segment at the tip of their tail. All other South Dakota snakes are born with a pointed tail. Rattlesnakes (along with copperheads and cottonmouths) are members of the Pit Viper family. The "pit vipers" have a triangular shaped head with a small cavity or pit on each side, between the eye and the nostril. They can sense warm-blooded prey in complete darkness up to 2 feet away. These thermoreceptor organs contain nerves that are sensitive to heat or warmth and can detect temperature differences within several thousandths of a degree.
The color of the Prairie Rattlesnake varies from light brown to green, with a yellowish belly. Dark oval blotches with light colored borders run along the center of its back. The blotches become crossbands on the back part of the body and rings around the tail. Adults will range in length from 30-40 inches, with a record of 57 inches. Three-foot rattlesnakes normally weigh 1 pound (a 54-inch snake weighed 3 1/2 pounds).
Many South Dakotans admit they have never seen a rattlesnake in the wild, even those in rattlesnake country. If they knew how many times they were within 10-15 feet of a snake, there would be many places to which they would never go back. The snakes are there; if you leave them alone, they will likely do the same to you. Snakes have a great display of camouflage. Most snakes are normally timid and secretive. When approached, they usually remain quiet to avoid detection. They may try to escape if given an opportunity. When frightened, cornered, or attacked, snakes will stand their ground and may attempt to strike at or even bite their intruder.
Rattlesnakes are cold-blooded or ectothermic animals. Their body temperature is influenced more by the temperature at the grounds surface where they are lying, rather than the air temperature. High or low temperatures cause the snakes to seek escape cover or shady areas. Most snakes cannot survive exposure to direct sunlight with temperatures over 100 degrees Fahrenheit, but rattlesnakes have a greater endurance to lower or freezing temperatures. Lethal temperatures for the snakes depend on the time of exposure. Unlike warm-blooded or endothermic animals, snakes are unable to produce their own body heat. To maintain a desirable temperature, snakes must rely on the temperature or warmth of their surroundings. The snake's circulatory/nervous systems aid in controlling the warming or cooling of their body.
With the harsh winter conditions in the northern states, rattlesnakes need to find an underground refuge for the winter months. Early fall frosts and shortening daylight, encourage snakes to move toward the dens, normally found on hillsides, bluffs, and rocky outcrops with underground openings used as denning sites. Snakes will also den up in holes or burrow systems of prairie dogs or other animals. Any such underground hole, crevice, mammal burrow, or other retreat area must be deep and extend to a depth below the frost line. The dens are normally found on hillsides with a southerly sun exposure allowing for spring and fall basking in the sun. Preferred dens are found on higher elevations above creeks and drainages that may be prone to spring flooding. Snakes cannot dig their own holes, although they can push or root out material with their noses. Vacant holes left behind by other animals are often used as escape cover or denning over the winter months. Snakes start their movements toward the den during the first freezing temperatures in the fall months, and will congregate near the den until the lower temperatures drive them underground. In late March or April, triggered by increasing ground temperatures, the snakes will move toward the ground surface or the den opening. With the warming nighttime temperatures and the prolonged period of sunlight, snakes leave the den to find food, mate, and have young during their summer travels. Throughout the summer months, the dens are abandoned and the snakes will travel 2-4 miles from their den. In a Wyoming study, radio transmitters were implanted in various snakes and one female rattlesnake traveled a distance of 8 miles from its den. Snakes return to the same den year after year, provided the den is not disturbed or destroyed. These dens or hibernacula have been used by many generations of snakes over the years. Some people feel that snakes leave scent trails or pheromones to identify past travels. Other snakes, such as juveniles, may use their sense of smell to follow the odor or pheromones trails of adult snakes, to locate their dens.
All snakes are predators and must locate their prey before they seize it. A snake's vision can detect movement out to about 40 feet; closer objects are seen more sharply. Rattlesnake eyes are lidless, but are protected by a hard transparent covering or scale. The pupil or the black portion of a rattlesnake's eye is elliptical, not round as with the nonvenomous snakes such as the racer. The vision of many snakes is better suited for nighttime searching rather than daytime activity. The eyes initiate the visual prey response, then the senses of smell or thermosensitivity come into play.
Rattlesnakes and other snakes lack external ear openings, but snakes are not deaf. Their outer body scales and bones are sensitive to air or ground vibrations. Snakes have two senses of smell: 1) external nostrils, lined with olfactory cells for picking up various odors, but the nose is mainly used for breathing and 2) the forked tongue, is their primary sensory organ for smelling. The tongue is a sensory device for the Jacobson's (vomeronasal) organ. This chemoreceptive organ lies within paired cavities on the roof of the snake's mouth. The snake extends its tongue, to pick up microscopic airborne particles and gases from the air on the tongues surface. The tongue then transfers these order stimuli into the Jacobson's organ and later the brain identifies them as food, enemy, or a mate. The tongue is also used for tracking the snakes prey. The food eaten by a snake depends upon the animal's size and the environment where it lives. Rattlesnakes eat animals such as mice, ground squirrels, and the young of prairie dogs or cottontail rabbits. They also eat other snakes, lizards, birds, and insects. The average snake will consume 2-3 times its own weight in various food items during the spring to fall months when the snake is away from its winter den.