Crotalus viridis
western rattlesnake

Crotalus viridis are found across most of the United States west of Texas and the Dakotas. They are also found in northern Mexico and southwest Canada. (Melli, 1999; LaDuc, 2000)

Crotalus viridis are found mostly in grasslands and prairies, and in brush. Various subspecies can also be found in woods, forests, caves, rock ledges, and alongside streams. Crotalus viridis avoids the desert. (LaDuc, 2000; Melli, 1999; Crotalus viridis viridis, 1999)

The various subspecies of Crotalus viridis may vary slightly in color. Most are greenish gray or greenish brown in color, although members of one subspecies are black with only slight markings. These rattlesnakes have from 33-55 dark blotches on their back, which flatten into rings on the tail, surrounded by lighter markings. Juviniles have similar markings to adults, but may have higher contrast in coloring. All Crotalus viridis have a rattle at the end of their tail, made up of segments of keratin, which knock together to make a rattling sound. The number of segments varies because each time the snake sheds its skin, it gains another segment. Crotalus viridis is generally about 91.5 cm in length, but can be from 89-114 cm. Males and females are dimorphic in that the number of rings on their tails differs. Males tend to have between 6-15 rings, and females tend to have between 4-11 rings.

There are nine subspecies of Crotalus viridis. Crotalus viridis viridis , or Western or Prairie rattlesnake, is the most widespread and is found in most regions of the species. There are eight others which are mostly named for the region they are found in. They are Grand Canyon rattlesnake (Crotalus viridis abyssus), Coronado Island rattlesnake (Crotalus viridis caliginis), Arizona Black rattlesnake (Crotalus viridis ceberus), Midget Faded rattlesnake (Crotalus viridis concolor), Southern Pacific rattlesnake (Crotalus viridis helleri), Great Basin rattlesnake (Crotalus viridis lutosus), and Hopi rattlesnake (Crotalus viridis oreganus). (LaDuc, 2000; Melli, 1999; Herp-edia, 1998; Reptiles and Amphibians of North Dakota, 1999)

Crotalus viridis are not aggressive. They usually flee if given the opportunity. They can be found in dense populations in some areas.

During winter and in cold areas, Crotalus viridis hibernate in caves or burrows of other animals. If hibernation places are scarce, as many as one hundred snakes may share one den. The snakes may even hibernate with other species. In warm weather, Crotalus viridis basks in the sun during the day, but in hot weather they seek shelter during the day and come out to hunt at night.

The predators of Crotalus viridis include some predatory birds such as the Red-tailed Hawk. When Crotalus viridis senses a predator, it makes a rattling sound to warn it. Smaller snakes tend to wait until the predator is closer to begin rattling, as do pregnant females.

Crotalus viridis use their eyes and sensory pits to detect prey and predators. Pits are heat sensing membranes between a snake's eye and nostril on both sides of its face. They can be used to find prey in the dark and can sense something up to 100 yards away. They also use their tongues to sense the chemicals in the air that are givin off by other animals; they flick their tongues in the air to accomplish this. (Greene, 1997; LaDuc, 2000; Melli, 1999; Reptiles and Amphibians of North Dakota, 1999)

Crotalus viridis eat small mammals, ground nesting birds, amphibians, and reptiles, including sometimes other snakes. They locate their prey by using their tongue to sense in airborn chemicals given off by the prey. Then they rapidly strike out at them, biting them with their fangs, then letting them go quickly. Venom is released from their fangs when the snakes strike. It works to immobilize the prey, which the snake then tracks and eats. The venom also works to destroy tissue and help with the digestion of bulkier prey.

Their venom is very deadly. Crotalus viridis use from 20-55% of their stored venom when they bite a small mammal such as a mouse. This is approximately 300 times the amount of venom needed to kill that animal. Venom is stored in glands which are connected to the hollow fangs. Venom is the means used to kill the prey, as the bite of the fangs alone would not usually result in death. The fangs are covered by thin tissue and fold back against the roof of the mouth when the mouth is closed.

During early spring and late fall when the weather is warm, Crotalus viridis hunts during the day. When the weather gets hotter, Crotalus viridis tends to seek shelter during the day and wait until night when it is cooler to hunt. (Greene, 1997; Jacobs, 1999; Kardong et. al., 1998; Kardong, 1996; Melli, 1999; Reptiles and Amphibians of North Dakota, 1999)

The only adverse affect that Crotalus viridis can have on humans is that they may bite an individual that provokes them. Their venom can cause injury and death. (Jacobs, 1999)

Crotalus viridis positively benefits humans economically by acting as a form of recreation in some areas. They are caught in rattlesnake roundups, the profits from which benefit the agencies who sponsor these events. They may also benefit humans by being a subject for scientific studies, which may economically benefit those who perform these studies. They also help to control populations of rodents and other animals that they feed on. (Fitch, 1998; Greene, 1997; Melli, 1999)

There are currently no conservation measures being taken for Crotalus viridis because their existence is not considered threatened. (Melli, 1999)

The name Crotalus comes from the Greek word "crotalon", which means "little bell", and is used to describe the rattle. The name viridis comes from the latin word for the color green.

Crotalus viridis can live up to twenty-one years. 95% of deaths of Crotalus viridis occur during the active season, rather than the winter. (Greene, 1997; Melli, 1999)