Western diamondback rattlesnake

Species of snake

The western diamondback rattlesnake or Texas diamond back (Crotalus atrox) is a rattlesnake species and member of the viper family, found in the southwestern United States and Mexico. Like all other rattlesnakes and all other vipers, it is venomous. It is likely responsible for the majority of snakebite fatalities in northern Mexico and the greatest number of snakebites in the U. S. No subspecies are currently recognized. 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 (the bushmasters, which attain probably similar weights and greater total length, occur up as far as Nicaragua). The color pattern generally consists of a khaki ground color, but it may also be pinkish or fallow, brick red, yellowish blonde, or white. This ground color is overlaid dorsally with a series of 23 45 (mean, 36) dorsal body blotches that are brown or a darker umber. The first of these may be a pair of short stripes that extend backwards to eventually merge. Some of the first few blotches on the back may be somewhat rectangular, but then become more hexagonal and eventually take on the distinctive diamond shape. The clarity of these markings is often blurred by small specks. The tail has two to eight (usually four to six) black bands separated by white or gray interspaces; this led to the nickname of "coontail", though other species (e. g., Mojave rattlesnake) have similarly banded tails. Its postocular stripe is gray or umber 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. The wide range of this species overlaps, or is close to, that of many others. It may be confused with them, but differences exist. The Mojave rattlesnake (C. scutulatus), also has tail rings, but the black rings are narrow relative to the pale ones. The timber rattlesnake (C. horridus), has no tail rings. In the western rattlesnake (C. oreganus), the pale tail rings are the same color as the ground. The tail of the black tailed rattlesnake (C. molossus), is a uniform black, or has indistinct tail rings. The Mexican west coast rattlesnake (C. basiliscus), also has a mostly dark tail with obscure or absent rings. The tiger rattlesnake, (C. tigris), has a relatively small head and large rattle along with a dorsal pattern consisting more of crossbands. The Middle American rattlesnake (C. simus), has a generally uniform gray tail without any rings, as well as a pair of distinctive paravertebral stripes running down the neck. Members of the genus Sistrurus lack tail rings and have enlarged head plates.

C. atrox is solitary except during the mating season, when males of the species are single minded and aggressive in pursuing females. Usually inactive between late October and early March, these ectotherms occasionally may be seen basking in the sun on warm winter days. In the winter, they hibernate or brumate in caves or burrows, sometimes with many other species of snakes. Active, alert, and large (most adults are between four and a half and five feet long), the western diamondback can administer a large amount of venom in its bite; it is not inclined to give ground when confronted. They are poor climbers. Natural predators include raptors such as hawks and eagles, roadrunners, wild hogs, and other snakes. When threatened, they usually coil and rattle to warn aggressors. They are one of the more defensive rattlesnake species in the US in the way that they stand their ground when confronted by a foe. If rattling does not work, then the snake will strike in defense.

A comprehensive study by Beavers (1976) on the prey of C. atrox in Texas showed, by weight, 94.8% of their prey consisted of small mammals. Birds, lizards, amphibians, fish, invertebrates, and mice are also preyed upon, with lizards mostly being eaten by young snakes. Avian prey include mockingbirds (Mimidae), quail, a nearly full grown Gambel's quail, a burrowing owl (Athene cunicularia),

A key participant in the food chain, it is an important predator of many small rodents, rabbits, and birds. In turn, it is preyed upon by a variety of larger mammals and birds, such as coyotes, foxes, hawks, and owls. Crotalus atrox can be active at any time of the day or night when conditions are favorable. It is primarily diurnal and crepuscular in spring and fall and becomes primarily nocturnal and crepuscular during the hot summer months. It is also an intermediate host of an intestinal acanthocephalan parasitic worm, Pachysentis canicola. They are one of the few species of snakes that engage in scavenging behavior.

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 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 700–800 mg. Severe envenomation is rare but possible, and can be lethal. Mortality rate of untreated bites is between 10 and 20%. They are also heavily collected from the wild, frequently being drawn out of their hiding places with gasoline and used in rattlesnake roundups, where they are killed for food, skins and entertainment. This Western diamondback rattlesnake may be the most common rattlesnake species found in homes and in direct conflict with human development in the American Southwest, particularly in the rapidly expanding metro areas of Phoenix and Tucson. Relocation of animals is seen as a sometimes controversial management solution.