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.
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 m). More commonly, this species of rattlesnakes grows to 3.5 to 4.5 feet (1.1-1.4 m). Average weight of the western diamondback ranges from 3-6 lbs (1.3-2.7 kg) with the largest species topping out around 15 lbs (6.7 kg). When provoked, the western diamondback takes the classic, raised S-shaped coil, as seen above, with its body flexed and ready to strike. More people are envenomated by the western diamondback rattlesnake that any other rattlesnake species in the United States.
Western diamondback rattlesnakes are a heavy bodied snake. A distinguishing feature of this snake is its triangular shaped head. Two dark diagonal lines are found on the snake's face running from the eyes to jaws. A dark, diamond-shaped pattern of scales run along the length of the snake's back. The scales found on the triangular head of this cold-blooded reptile are small while the scales located on the back are larger.
Western diamondback rattlesnakes are pit vipers. Their heat sensing openings, known as a loreal pits, are located on each side of their head just behind their nostrils. These are the external openings to an extraordinarily sensitive infrared detection organ that allows the western diamondback rattlesnake to become aware of temperature differences of other living organisms that can be only a fraction of a degree apart. This organ allows the rattlesnake to recognize the heat given off by other animals helping it to recognize both predators and prey. In addition, the loreal pits, seen above, 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.
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 6500 ft (2,000 m). One final distinguishing feature of the western diamondback is the four to six alternating black and white bands, shown above, found on the tail just prior to the beginning of the rattle.
Western diamondback rattlesnakes are most active from early spring through late fall. They overwinter with other western diamondbacks, hibernating, often 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 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 cm). Their fangs often break off inside the prey animals but they have reserve fangs that replace the lost fangs. The fangs are naturally replaced 2 to 4 times each year. Western diamondbacks only need to feed once every 2-3 weeks.
Western diamondback rattlesnakes are highly venomous and their bites are potentially life-threatening to humans. They do not rattle every time before they strike especially if they are startled themselves 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 diamondback 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 three foot (1 m) long snake has a strike radius of about 18 inches (.5 m). In captivity, western diamondback rattlesnakes can live from 15-20 years.
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 9-15 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.
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 cannot 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.
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 witch craft. 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 remember this holy and/or dangerous reptile. The petroglyph shown above of a coyote and rattlesnake is found in Petroglyph National Monument in New Mexico.
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 again 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.