Description: The color pattern generally consists of a dusty-looking gray-brown ground color, but it may also be pinkish-brown, brick red, yellowish, pinkish, or chalky white. This ground color is overlaid dorsally with a series of 23 to 45 (mean, 36) dorsal body blotches that are dark gray-brown to brown in color. The first of these may be a pair of short stripes that extend backwards to eventually merge. Some of the first few blotches may be somewhat rectangular, but then become more hexagonal and eventually take on a distinctive diamond shape, hence the name "diamondback rattlesnake". The tail has two to eight (usually four to six) black bands separated by ash white or pale gray interspaces; this led to the nickname of "coon tail", though other species (e.g., Mojave rattlesnake) have similarly banded tails. Its postocular stripe is smoky gray or dark gray-brown and extends diagonally from the lower edge of the eye across the side of the head. This stripe is usually bordered below by a white stripe running from the upper preocular scale down to the supralabial scales just below and behind the eye. Its off-white belly is usually unmarked, its anal scale is undivided, and its dorsal scales are extremely keeled, often in rows of 25 to 27 near the midbody.

Adults commonly grow to 4 feet in length. Specimens over 5 feet are infrequently encountered, while those over 6 feet are very rare, and the largest reported length considered to be reliable is 7 feet. Males become much larger than females, although this difference in size does not occur until after they have reached sexual maturity. Rattlesnakes of this species considered medium-sized weigh up to 3 to 6 lbs., while very large specimens can reportedly weigh up to 15 lbs. Overall, it is probably the second largest-bodied species of rattlesnake, behind only its close cousin the eastern diamondback rattlesnake, and is also the second largest of North American venomous snakes.

Habitat: Its habitats range from flat coastal plains to steep rocky canyons and hillsides; it is associated with many different vegetation types, including desert, sandy creosote areas, mesquite grassland, desert scrub, and pine-oak forests. It is common to see the western diamondback on rural blacktop roads in early evening, because of the heat retention of these surfaces, as ambient temperatures drops.

Range: In the United States, it occurs in central and western Arkansas, Oklahoma excluding the northeast, north-central region and the panhandle, Texas excluding the northern panhandle and the east, southern and central New Mexico and Arizona, extreme southern Nevada, southwestern Utah, and in southeastern California on either side of the Chocolate Mountains. Records from extreme southern Kansas (Cowley and Sumner Counties) may be based on a natural occurrence of the species, while multiple records from near Kanopolis Reservoir in Ellsworth County seem to indicate a viable (although isolated) population.

Found in these States: AR | AZ | CA | KS | NM | NV | OK | TX

Venom: Like most other American pit vipers, the venom contains proteolytic enzymes. Proteolytic venoms are concentrated secretions that destroy structural tissues and proteins via catabolism, which help in disabling prey. The venom of C. atrox is primarily hemotoxic, affecting mainly the blood vessels, blood cells and the heart. The venom contains hemorrhagic components called zinc metalloproteinases. The venom also contains cytotoxins and myotoxins which destroy cells and muscles, adding to the damage to the cardiovascular system. In addition to hemorrhage, venom metalloproteinases induce myonecrosis (skeletal muscle damage), which seems to be secondary to the ischemia that ensues in muscle tissue as a consequence of bleeding and reduced perfusion. Microvascular disruption by metalloproteinases also impairs skeletal muscle regeneration, being thereby responsible for fibrosis and permanent tissue loss. General local effects include pain, heavy internal bleeding, severe swelling, severe muscle damage, bruising, blistering, and necrosis; systemic effects are variable and not specific, but may include headache, nausea, vomiting, abdominal pain, diarrhea, dizziness, and convulsions. Bleeding caused by hemorrhagins is a major clinical effect that can be fatal.

This species has LD50 values of 2.72 mg/kg intravenous, 20 mg/kg intramuscular and 18.5 mg/kg subcutaneous, which is far less toxic than many other rattlesnakes. However, because of its large venom glands and specialized fangs, the western diamondback rattlesnake can deliver a large amount of venom in a single bite. The average venom yield per bite is usually between 250 and 350 mg, with a maximum of 700 to 800 mg. Severe envenomation is rare but possible, and can be lethal. Mortality rate of untreated bites is between 10 and 20%.

Diet: Birds, lizards, amphibians, fish, invertebrates, and mice are also preyed upon, with lizards mostly being eaten by young snakes.

Reproduction: Rattlesnakes, including C. atrox, are viviparous. Gestation lasts six or seven months, and broods average about a dozen young. However, the young stay with the mother for only a few hours before they set off on their own to hunt and find cover, so that the mortality rate is very high. Mating occurs in the fall, and the females give birth to as many as 25 young, which may be as long as 12 inches. The young are fully capable of delivering a venomous bite from the moment they are born.

Status: Listed as Least Concern in view of its wide distribution, presumed large population, and because it is unlikely to be declining fast enough to qualify for listing in a more threatened category.

Taxonomy: