Diverse ecosystem

The American West is a kaleidoscope of varied landscapes and ecological environments. From vast sand-covered deserts to sweeping valleys covered with the sparse vegetation of a variety of bur sage or a sea of aromatic creosote bush, Larrea tridentata, to high mountain peaks of rugged, metamorphic schist and mountain ridges strewn with boulders of granite — the American West is a distinct and remarkable place. So too are the unique animals that have evolved to survive and thrive in these varied and harsh lands. No better illustration is found of such adaption and survival than by looking at the life story of the western diamondback rattlesnake, Crotalus atrox. (Image credit: Linda & Dr. Dick Buscher)

A big specimen

The western diamondback rattlesnake is the largest of the 32 known species of rattlesnakes found in North America, capable of growing to a length of 8.5 feet (2.6 meters). More commonly, this species grows to between 3.5 and 4.5 feet (1.1 and 1.4 m). Average weight of the western diamondback ranges from 3 to 6 lbs. (1.3 to 2.7 kilograms), with the largest species topping out around 15 lbs. (6.7 kg). When provoked, the western diamondback takes the classic, raised S-shaped coil, with its body flexed and ready to strike. More people are envenomated by the western diamondback rattlesnake than any other rattlesnake species in the United States. (Image credit: NPS)

Distinguishing features

Western diamondback rattlesnakes are a heavy bodied snake with a distinct, triangular-shaped head. Two dark diagonal lines run across the snake's face, from the eyes to jaws. A dark, diamond-shaped pattern of scales decorates the length of the snake's back. These scales are larger than the ones found on the triangular head of this reptile. (Image credit: NPS)

Snake skills

Western diamondback rattlesnakes are pit vipers. So-called loreal pits, which are located on each side of the head just behind the nostrils, form the external openings to an extraordinarily sensitive infrared detection organ. That organ allows the western diamondback rattlesnake to detect the teensiest of temperature differences in the heat given off by other living organisms. In that way, the rattlesnake can detect both predators and prey. In addition, the loreal pits (shown here) act as thermal regulating system, helping the western diamondback to maintain a proper body temperature. Western diamondback rattlesnakes also have slit-shaped eye pupils, common in most poisonous snakes. (Image credit: NPS)

Notable markings

Western diamondback rattlesnakes have a wide distribution across the American states of California, Arizona, New Mexico, Oklahoma and Texas as well as the northern half of Mexico. They are found in a variety of habitats, from arid deserts to rocky mountainous environments. Biologists actually consider them to be ecological generalists, successfully surviving from elevations ranging from below sea level to 6,500 feet (2,000 m).One final distinguishing feature of the western diamondback is the four to six alternating black and white bands found on the tail just prior to the beginning of the rattle. (Image credit: NPS)

Patient critter

Western diamondback rattlesnakes are most active from early spring through late fall. They overwinter with other western diamondbacks, often hibernating in large numbers, in underground or deep, rocky crevice dens. In the extreme heat of summer, they are commonly active only from dusk to shortly after sunrise, while spending the daylight hours resting under a shady bush or in an underground burrow. They often remain in one area for many days, patiently waiting to ambush prey.Their favorite prey animals are small mammals such as local rabbits, ground squirrels, mice and an occasional bird. The poisonous venom, injected through two hollow, grooved fangs, quickly immobilizes the prey. The snake then approaches the prey and swallows its victim whole. Their fangs are attached to the upper jaw by a hinge so that they can fold them into the mouth when not in use. This folding ability allows rattlesnakes to have some of the longest fangs of all venomous snakes, some reaching a length of 2 inches (5 centimeters). Their fangs often break off inside the prey animals, but they have reserve fangs that replace the lost ones. The fangs are naturally replaced two to four times each year. Western diamondbacks only need to feed once every two to three weeks. (Image credit: NPS)

Warnings, sometimes

Bites from a western diamondback are potentially life-threatening to humans. The snakes don't always rattle before they strike, especially if they are startled or if they are cold. The sound of the rattle is more like a "buzz," but such warning should always be heeded. Just like human hair and fingernails, the diamondback's rattle is made up of keratin. A new segment of the rattle is added each time the snake sheds. But diamondbacks shed at different rates and the segments of their tails can break off; so it is not possible to determine the age of a diamondback by counting the segments of its tail.Western diamondbacks are capable of vibrating their rattle at a speed of 60 times each second. Their striking distance can cover about one-third to one-half of their body length. A 3-foot-long (1 m) snake has a strike radius of about 18 inches (0.5 m). In captivity, western diamondback rattlesnakes can live from 15 to 20 years. (Image credit: NPS)

Different reproductive process

Western diamondback rattlesnakes reach sexual maturity at 3 years of age. Courtship and mating of western diamondbacks most commonly occurs in the spring. Gestation lasts about 167 days. The female diamondback carries her eggs internally until they are ready for live birth in July or August. Western diamondbacks are ovoviviparous, with the young piercing their thin egg membrane immediately before birth The female will then give birth to nine to 15 babies. Large diamondback females have been known to give birth to 20 or more young. The young rattlesnakes scatter from their mother within a few hours after their birth in search of food and shelter. (Image credit: NPS)

A dangerous brood

Baby western diamondback rattlesnakes are about 10 inches (25 cm) long at birth. Because of the pattern and color of their scales, they tend to blend in perfectly with the rugged desert environments. For that reason, these young rattlesnakes are sometime locally called the "invisible snake."Young diamondbacks are not born with their rattles developed and thus are not capable of giving a warning before they strike. They are born with what is known as a "pre-button," but that can't yet make that infamous warning sound. Young western diamondback rattlesnakes begin to develop their rattles after the second skin shed. Because of their small size, the newly born western diamondback young are very vulnerable to birds of prey, other snakes and carnivorous mammals. (Image credit: AZ Game & Fish)

Stuff of legend

Rattlesnakes have long been a part of the legends and lore of the Native American people who lived in the rugged desert lands of North America. Most often, they were viewed as powerful and dangerous; and some cultures even associated them with witchcraft. Some tribes designated family groups with clan animals, and snake clans are found among the Hopi and Zuni people of Arizona and New Mexico. Many tribes seemed to have used the potential danger of rattlesnakes in stories to warn their children to behave and to follow the tribal and cultural norms. Across the vast homelands of the western diamondback rattlesnake, petroglyphs carved long ago honor and commemorate this holy and/or dangerous reptile. The petroglyph shown here of a coyote and rattlesnake is found in Petroglyph National Monument in New Mexico. (Image credit: NPS)

Losing land

The loss of natural habitat by expanding desert communities is the greatest threat to the western diamondback rattlesnake. Fortunately for these magnificent snakes, much of their natural habitat still lies in areas of extreme dryness and heat. Cultural biases against snakes in general also results in too many diamondbacks simply being killed when seen. Natural predators of the western diamondback include bobcats, foxes, roadrunners, coyotes, hawks and eagles. Large hoofed animals, such deer, antelope, cows and horses are also a danger, as they can easily trample the large snakes. (Image credit: NPS)

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