Western diamondback rattlesnake

Appearance

Adults commonly grow to 120 cm in length. Specimens over 150 cm are infrequently encountered, while those over 180 cm are very rare. The maximum reported length considered to be reliable is 213 cm . 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 weighed 1.8 to 2.7 kg , while very large specimens can reportedly weigh up to 6.7 kg .

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 24-25 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. The tail has two to eight black bands separated by ash white or pale gray interspaces; this led to the nickname of "coon tail", though other species 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.

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 Mohave 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.

Naming

Common names for this species include: western diamondback rattlesnake, western diamond-backed rattlesnake, adobe snake, Arizona diamond rattlesnake, coon tail, desert diamond-back, desert diamond rattlesnake, fierce rattlesnake, spitting rattlesnake, Texan rattlesnake, and Texas diamond-back.

Status

This species is classified as Least Concern on the IUCN Red List . Species are listed as such due to their wide distribution, presumed large population, or because they are unlikely to be declining fast enough to qualify for listing in a more threatened category. The population trend was stable when assessed in 2007.

They are also heavily collected from the wild, frequently being drawn out of their hiding places with gasoline, and used in Rattlesnake Round-Ups, where they are killed for food, skins, and entertainment.

Behavior

''C. atrox'' are solitary except during the mating season. Usually inactive between late October and early March, occasionally these ectotherms 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. Life expectancy is more than 20 years.

They are poor climbers. Natural predators include raptors such as hawks, eagles, roadrunners, and other snakes. When threatened, they usually coil and rattle to warn aggressors. They are one of the more aggressive rattlesnakes 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.

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. Towards the southern

Reproduction

Rattlesnakes, including ''C. atrox'', are viviparous. Gestation lasts six or seven months, and broods average about a dozen young. However, the young only stay with the mother for a few hours before they set off on their own to hunt and find cover, thus 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 30 cm . The young are fully capable of delivering a venomous bite from the moment they are born.

Defense

Like most other American pit vipers, the venom contains proteolytic enzymes. Proteolytic venoms are concentrated secretions that destroy tissues as a result of catabolism of structural and other proteins, 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 that add to the failure of the cardiovascular system. In addition to hemorrhage, venom metalloproteinases induce myonecrosis , 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 therefore responsible for fibrosis and permanent tissue loss after bites from this species. 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. Hemorrhagins causing bleeding is a major clinical effect.

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 significant 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%.