Rattlesnakes belong to the pit viper family Crotalidae, so named because all possess visible loreal pits, or lateral heat sensory organs, between eye and nostril on each side of the head. These heat sensory pits are not present in true vipers, which do not occur in the Western Hemisphere. The facial pits enable rattlesnakes to seek out and strike, even in darkness, warm objects such as small animal prey, as well as larger animals that could be a threat. The vertically elliptical eye pupils, or “cat eyes,” are also a characteristic of rattlesnakes. Identifying a dead rattler whose rattles are missing can be done by looking at the snake’s scaleson the underside in the short region between the vent and the tip of the tail If the scales are divided down the center, the snake is harmless. The scales on rattlesnakes are not divided.
Rattlesnakes come in a great variety of colors, depending on the species and stage of molt. Most rattlers are various shades of brown, tan, yellow, gray, black, chalky white, dull red, and olive green. Many have diamond, chevron, or blotched markings on their backs and sides.
Range and Habitat
Rattlesnakes occur only in North and South America and range from sea level to perhaps 11,000 feet (over 3,000 m) in California and 14,000 feet (4,000m) in Mexico, although they are not abundant at the higher elevations. They are found throughout the Great Plains region and most of the United States, from deserts to dense forests and from sea level to fairly high mountains. They need good cover so they can retreat from the sun. Rattlers are common in rough terrain and wherever rodents are abundant.
FoodYoung or small species of rodents comprise the bulk of the food supply for most rattlesnakes. Larger rattlers may capture and consume squirrels, prairie dogs, wood rats, cottontails, and young jackrabbits. Occasionally, even small carnivores like weasels and skunks are taken. Ground-nesting birds and bird eggs can also make up an appreciable amount of the diet of some rattlers. Lizards are frequently taken by rattlers, especially in the Southwest. The smaller species of rattlesnakes and young rattlesnakes regularly feed on lizards and amphibians.
Rattlesnakes consume about 40% oftheir own body weight each year. Many prey are killed but not eaten by rattlesnakes because they are too largeor cannot be tracked after being struck. One male rattler captured in the field had consumed 123% of its weight, but young rattlers frequently die due to lack of food. Domestically raised rattlesnakes will survive when fed only once a year, but in the field, snakes usually feed more than once, depending on the size of prey consumed. A snake may kill several prey, one after another, and of different species. When rodents and rabbits are struck, the prey is immediately released. The snake then uses its tongue to track the prey to where it has died.
Rattlesnakes are distinctly American serpents. They all have a jointed rattle at the tip of the tail, except for one rare species on an island off the Mexican coast. This chapter concerns the genus Crotalus, of the pit viper family Crotalidae, suborder Serpentes. Since snakes evolved from lizards, both groups make up the order Squamata. This article describes the characteristics of the common species of rattle snakes that belong to the genus Crotalus. These include the eastern diamondback, (Crotalus adamanteus); the western diamond (back) rattlesnake, (Crotalus atrox); the red diamond rattlesnake, (Crotalus ruber); the Mohave rattlesnake, (Crotalus scutulatus); the sidewinder, (Crotalus ceraster); timber rattlesnake, (Crotalus horridus); three subspecies of the western rattlesnake, (Crotalus viridis): the prairie rattlesnake (Crotalus v. viridis); the Great Basin rattlesnake (Crotalus v. lutosus); and the Pacific rattlesnake (Crotalus v. oreganus).
There are 15 species of rattlesnakes in the United States and 25 in Mexico. Other front-fanged poisonous snakes of the Crotalidae family, which are n included in this discussion, are the massasauga and pigmy rattlesnakes, both of the genus Sistrurus. Also not included are two snakes that do not have rattles, hence are not called Ratt snakes: the water moccasin or cotton mouth, and the copperhead, both of the genus Agkistrodon. Two other gen era of poisonous snakes in North America are coral snakes (Micrurus and Micruroides) of the family Elapidae.