Rattlesnakes

The snake is an animal.
It has a backbone and heart.
It has red blood and drinks water and eats food.
It breathes air and feels fear,
just like every other animal in the world.
And it's in a body that is the hardest thing
for the average person to understand.
—Dave Barker, herpetologist

The earliest North American pit vipers lived approximately 5 million years ago. They have evolved to inhabit a wide variety of habitats, from open desert sand dunes to northern prairie to subtropical scrub. All of the lower 48 states are home to at least one species of rattlesnake, with the greatest diversity of species occurring in the southwestern portion of the country.

Unique Abilities

Rattlesnakes are equipped with a remarkable set of specialized sensory organs. While rattlesnakes lack the ability to hear in the normal sense, as they have no external ear, they are sensitive to vibrations transmitted through the ground. They do not have eyelids; instead, the eyes are protected by a transparent covering that is shed with the skin. Rattlesnakes derive a considerable amount of information about their environment through the air, both through the use of olfactory cues via the nostrils, and through the use of their forked tongue, which transfers "tastes" from the surrounding air to organs located in the roof of the mouth.

Perhaps most remarkable is the ability of rattlesnakes to "see" heat through the use of facial pits located between the eyes and nostrils. These organs are so sensitive that they present the snake with a thermal picture of an animal, possibly allowing it to distinguish between a potential prey animal and a potential predator, even in complete darkness. In the light, the thermal image is superimposed over the visual image in the brain of the animal.

The fangs of rattlesnakes lie folded against the roof of the mouth when not in use. These structures resemble hypodermic needles, being hollow down to their tip. In the act of striking, the fangs are rotated forward and out. Fangs last between six to ten weeks before they are replaced by one of up to seven sets in various stages of development behind the ones in use.

Vulnerable Homebodies

In the northern areas of their range and at higher elevations, timber rattlesnakes, western rattlesnakes, and western diamondback rattlesnakes congregate in the fall at crevices in rocky ledges to hibernate for the winter. Rattlesnakes return to these sites every year. Rattlesnakes exhibit denning behavior in northerly latitudes, presumably because a long period of dormancy during the winter is necessary, and there are relatively few sites sufficiently sheltered for them to survive. Unfortunately, denning behavior also renders whole populations vulnerable to rapid extermination, and the habitat is ruined for years after human intrusion.

Helpful to Ecosystems and Humans

Rattlesnakes help control rodents such as mice, rats and prairie dogs, which can damage crops and spread disease if their numbers are not checked by natural predators. Rattlesnakes are, in turn, fed upon by a wide variety of predatory birds.

Conservation Status

Out of 16 species of rattlesnakes native to the United States, seven have been listed as threatened or endangered in one or more of 15 different states. Commercial exploitation, either for skins, gallbladders or for the live animal trade, is at least partially responsible for the endangerment of these species. In most parts of the country, the specialized habitats that rattlesnakes require for winter denning sites, and also for protection from excessive heat and fires, are becoming increasingly scarce.

Few states classify rattlesnakes as pests or vermin, but neither are they afforded game status in keeping with their commercial value and the hunting pressures placed upon them.

Commonly Exploited Species

The species most commonly targeted by rattlesnake roundups and the skin-and-parts trade in the United States are the western diamondback rattlesnake, the prairie or western rattlesnake, the eastern diamondback rattlesnake, the timber or canebreak rattlesnake, and, to a lesser extent, the black-tailed rattlesnake. Roundups in Pennsylvania also target the copperhead and use nonvenomous species in certain contests.

Eastern Diamondback Rattlesnake (Crotalus adamanteus)

The eastern diamondback rattlesnake ranges along the coastal lowlands of southeast North Carolina to extreme eastern Louisiana, including all of Florida and its keys. The species is extremely rare in Louisiana and may be functionally extinct in that state. The eastern diamondback lives in longleaf pine forests, coastal longleaf pine/wiregrass sandhills and clayhills, flatwoods, sand pine scrub, and tropical hardwood hammocks. Much of this original habitat is now severely reduced in range, particularly longleaf pine forests. This species makes extensive use of gopher tortoise burrows and tree stumps as winter refuge sites, both of which are in increasingly short supply due to the decrease in gopher tortoise populations and to stump removal as a part of logging practices.

The species is believed to be in decline across its range. Habitat loss and excessively high hunting pressures are widely blamed for the decrease in its numbers.

Western Diamondback Rattlesnake (Crotalus atrox)

This species is the most common target of roundups in Oklahoma and Texas. In the United States, its range encompasses western central Arkansas and Texas to southeastern California. It is found in a wide variety of habitats, from lowlands to mountains up to 5,000 feet.

The western diamondback rattlesnake also comprises the bulk of the take for the skin trade and for gallbladders exported to Asia. The states of New Mexico, Oklahoma, and Texas do not monitor the trade in this species, beyond one ongoing study at Sweetwater, Texas. Estimates as to the trade in this species run as high as 100,000 individuals for roundups alone, but this estimate may be high because it is based on the existence of 50 roundups; the current number is closer to 20 in Oklahoma and Texas. Confounding the issue is that trade in this species occurs throughout the year, and animals brought in to roundups are probably only about 15 percent of all of those taken for the skin, meat, gallbladder, and curio trade.

Timber Rattlesnake (Crotalus horridus)

The distribution of the timber rattlesnake covers 27 states, from New Hampshire south to the Appalachians to northern Florida, eastern Texas, Oklahoma, Kansas, southeastern Minnesota, eastern Wisconsin and southern Illinois, Indiana, and Ohio. Its numbers have been significantly reduced in the following 20 states: Alabama, Connecticut, Georgia, Illinois, Indiana, Iowa, Kansas, Maryland, Massachusetts, Minnesota, Nebraska, New Hampshire, New Jersey, New York, North Carolina, Ohio, Pennsylvania, South Carolina, Vermont, and Wisconsin. The timber rattlesnake was extirpated from Maine in the 1860s and from Rhode Island in the 1970s. It formerly occurred in southern Ontario, Canada, but it is believed to have been extirpated there for more than 50 years. The species is listed as endangered in Connecticut, Massachusetts, New Hampshire, New Jersey, Vermont, and Virginia, and as threatened in New York and Texas.

There is no doubt that human disturbance and intentional harassment have led to a severe reduction in the number of remaining populations of this species, as well as to a reduction of individuals within remaining populations.

Western or Prairie Rattlesnake (Crotalus viridis)

The western or prairie rattlesnake ranges from western Iowa to California and Oregon, southern Canada, and south to northern Mexico. This species inhabits open grasslands and congregates in rock ledges during the winter. Populations of this species become highly concentrated in winter denning sites, rendering the species particularly vulnerable to extirpation. Evidence suggests that females usually become reproductive at four or five years and breed twice a year. Consequently, den raiding, which is the most common method for the collection of the western or prairie rattlesnake, may be particularly harmful to this species. In one study, a researcher monitored seven C. viridis dens that were hunted repeatedly for periods ranging from 14 to 24 years. When the hunts began, some of the dens produced as many as 89 snakes in a single raid. In later years, three of the dens no longer contained any snakes, and the largest number of snakes obtained in any single raid was eight. Roundups and their associated den site disturbance clearly pose a threat to this species.