Resource: Rattlesnakes

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Rattlesnakes are venomous snakes that inhabit sandy deserts, rocky hillsides, and grassy plains over a range that extends from southern Canada to northern South America. They are especially common where rodents, their favorite prey, are abundant. Of the 16 rattlesnake species in the U.S., six inhabit the Southwest, including the three featured in this video—the Mohave rattlesnake, the Horned rattlesnake, and the Western Diamondback rattlesnake.

Rattlesnakes have two distinguishing features: a triangular head and a tail rattle, which is made of ringed segments of a fibrous protein called keratin. Keratin is the same substance contained in the snake's scales. In fact, the rattle forms from skin that has been shed. Each time a rattlesnake molts, it adds a segment to the rattle.

Rattlesnakes belong to the pit viper family. Pit vipers have heat-sensitive cavities, or pits, on the sides of their heads that detect subtle changes in temperature, as occurs when a warm-blooded animal is near. They process heat as a visual image in their brains, allowing them to distinguish predator from prey, even at nighttime. Knowing this helps rattlesnakes determine whether to go on the defensive or attack. When a rattlesnake moves its rattle back and forth—at a rate of more than 60 times per second—the ringed segments bump against each other and produce the sound. This sound is a warning signal to potential predators to stay clear of the snake. However, when the snake decides to attack, it waits quietly for the animal to come near.

Some snakes kill their prey by squeezing the animal to death. Rattlesnakes kill theirs with venom, a toxic saliva that they inject into their prey's skin through two long, curved, hollow fangs. A duct connects each fang to a gland on either side of its head that produces the venom. Snake venom is a mixture of enzymes that destroy blood cells and tissue (hemotoxins) or paralyze nerves (neurotoxins). Most rattlesnake venom contains more hemotoxins than neurotoxins. The venom is not only lethal but contains enzymes that jump-start the digestive process. This early start is important, because rattlesnakes—like all snakes—swallow prey whole. They have the ability to unhinge their top and bottom jaws, which allows them to eat animals that are wider than their mouth openings. This means that digestion can take a long time. And because the digestive process is energy-intensive, a rattlesnake may become sluggish after eating and is therefore an easier target for predators.

Rattlesnakes deliver venom when needed, but not with every bite. In fact, as many as half of all rattlesnake bites may be "dry," or venomless. A dry bite serves as a means of protection—a warning to another animal to stay away. In this way, the snake preserves its venom supply for hunting prey. Even without venom, a rattlesnake bite can be extremely painful.

To learn more about a snake's unique jaw structure, check out Unhinged!.

To learn more about desert conditions and inhabitants, check out Desert Biome.

To learn about other animals that inhabit the desert southwest, check out Bighorn Sheep, Bats of the Southwest, Burrowing Owl, Horned Lizard, Phainopepla Bird, and Tarantulas.

Print Questions for Discussion

• When during the year are rattlesnakes active? What environmental factors determine their activities?
• What are rattles made of? How do they make their sound?
• How much venom is released in a rattlesnake bite?
• Describe the movement of the rattlesnake. How does this locomotion style improve its chances of survival?
• What are some ways in which rattlesnakes protect themselves from extreme heat?