Characteristics The Prairie Rattlesnake (Crotalus viridis) is a venomous pit viper with a diamond shaped head on a relatively thin neck. This leads to a fairly heavy body that can grow to five feet in length. The pupils of the eyes are vertically elliptical. There is a heat sensitive pit between the eye and the nostril on each side of the head.
The body color ranges from tan to green or brown with 33-55 distinctive blotches down the back, which flatten into rings on the tail. The blotches are brown to dark brown with a dark brown to black border and there is often a trace of white separating the blotches from the basic body color. Smaller spots are along the sides below the blotches. The belly is light yellow to cream. The scales are keeled down the middle. The tail ends in a rattle which represents not age in years but the number of times the snake has shed its skin.
Watch Your Hands And Feet The faster the snake grows the more often it has to shed its skin. Sometimes some of the rattles may break off. When frightened, the snake uses the muscles at the base of the rattle to vibrate or shake the rattle segments together which produces the sound. There is nothing in the rattles to make the sound.
Most rattlesnakes will take a defensive position when cornered or provoked and rattle to warn of their presence, but they don’t always rattle before they strike in defense. It is always a good idea to watch where one puts their hands and feet when in rattlesnake country.
Rattlesnakes have a broad prey base consisting of ground squirrels, mice, rats, small rabbits and prairie dogs, ground nesting birds, amphibians, lizards and even other snakes. They locate their prey by sight and then are aided by their senses of smell and thermosensitivity. The external nostrils are lined with olfactory cells which pick up odors, but the nostrils are used primarily for breathing.
The forked tongue flicks in the air picking up microscopic particles and gases and then transfers them to the Jacobson’s organ which lies within paired cavities in the roof of the mouth. Then the brain interprets whether it is food, enemy or mate.
Venom Delivery The rattlesnake has a pair of hollow fangs for delivering its venom. The long, curved fangs fold against the roof of the mouth when not in use, but point forward when the snake strikes its target. Broken fangs are replaced as the snake has a number of fangs in various stages of growth. In fact fangs and other teeth are regularly replaced. The snake controls the amount of venom injected by the contraction of muscles surrounding the venom glands.
They often inject 20-50% of their stored venom which is many times the amount needed to kill their prey. The venom immobilizes and kills the prey by acting as a hemotoxin affecting the blood and lymphatic systems causing pain and swelling. The snake coils and strikes up to half the snakes body length. Once the venom is injected the snake lets the prey go and then tracks the prey by scent and ingests it whole.
Prey As Well As Predator The rattlesnake itself is prey as well. A number of predatory birds such as the Red-tailed Hawk will prey on rattlesnakes. Badgers too will feed on rattlesnakes. Even when rattlesnakes swim on lakes as has been observed on Bighorn Lake, they are not safe. Young rattlesnakes have been found in the stomachs of rainbow trout. Rattlesnakes have to be especially careful around humans.
As they are cold blooded, they are greatly influenced by temperature and more by ground temperature than air temperatures. In cooler weather they will be more active during the day, but when temperatures soar into the 90 degrees F and over a hundred they will become more nocturnal with senses well adapted to do so.
When the harsh winter conditions start, the snakes will have to find refuge underground in dens that extend below the frost line. Rattlesnakes hibernate communally, sometimes in large groups and sometimes with other species. They will usually emerge from hibernation in April or May. They will use the same den year after year.
Territory The prairie rattlesnake has the largest range of any rattlesnake in the country. They range from border to border in the western half of the Great Plains states and into the Rocky Mountain states from Montana to New Mexico. The only exception is some of the higher elevations of Colorado and Wyoming, extending a short ways into Canada and Mexico as well. They seem to prefer dry, rocky areas with moderate vegetation and grasslands and prairie, but can also be found in woodlands, forests and caves.
Mating In early summer, males start searching for available females for mating. Size, fighting, and mate persuasion are not the critical factors, but rather the ability to successfully search for females. Straight line searching apparently is the most successful method. They have internal fertilization and are viviparous which means they give birth to live young instead of laying eggs.
Giving Birth And Young Rattlers
They can produce anywhere from 1 to 25 young with the typical being in the 4 to 12 range. The young are born between August and October.
The 9 to 11 inch young look like the adults although their color is often more vivid.
They are able to take care of themselves and need no parental care as they are already venomous.
They become sexually mature at age three or older but will not necessarily mate every year.
Gravid females rarely hunt and will sometimes gather in aggregates to bask in the sun while waiting to give birth.
Avoiding A Bite Some studies have shown that over half of the people bitten by rattlesnakes are bitten in the wrist or forearm. This is surprising since the wrist and forearm of most people is not within the striking range of rattlesnakes, but that is when they are standing. Other studies have shown that over a third of the people bitten were trying to catch, handle or kill the snake.
One recent case involved the severed head of a rattlesnake. In any case seek prompt medical attention. Hopefully through better education the “kill any snake” mentality can be replaced with an understanding of their beneficial role in the natural world.
Last updated: February 24, 2015
Bighorn Canyon National Recreation Area South District Visitor Center
20 US Hwy 14A
(307) 548-5406 is the South District in Lovell, WY.
(406) 666-9961 is the North District in Fort Smith, MT.