Western diamond-backed rattlesnake (Crotalus atrox)
|Also known as:||Western diamondback rattlesnake|
|Size||Average length: 91 – 122 cm (2)|
Maximum length: up to 224 cm (2)
Classified as Least Concern (LC) on the IUCN Red List (1).
An iconic reptile, the rattle of the western diamondback rattlesnake is one of the most evocative sounds of the arid southern United States (3). A large and heavy-bodied species, the western diamond-backed rattlesnake’s colouration varies from chalky grey to dull red, appearing dusty due to minute flecks and dots on the scales. As suggested by its common name, this species has diamond-shaped markings over most of its body, which are edged with black and white (2). These markings are replaced by conspicuous black and white bands towards the rear of the tail, just in front of the rattle (2) (4), while the head has two characteristic pale stripes, one in front of the eye and the other behind, which run diagonally down the head towards the mouth (2). Undoubtedly, the most distinctive feature of this species is the rattle. This unusual appendage is composed of loosely-connected, interlocking segments made of dead, horny keratin, which knock together when the tail is vibrated, producing the rattling sound (4) (5). Newborn rattlesnakes are born without a rattle, but acquire segments after each moult, eventually developing as many as ten (4) (5).
The western diamond-backed rattlesnake inhabits the southern USA, and northern and central Mexico. In the USA, it can be found in south-eastern California, southern Nevada, Arizona, New Mexico, Texas, Oklahoma and Arkansas, while in Mexico, it occurs in extreme north-east Baja California, and northern states, south as far as Veracruz, and possibly Oaxaca (1)
The western diamond-backed rattlesnake can be found in arid and semi-arid habitats, including desert, plains, rocky hills, grassland, shrubland, woodland, dried river beds and coastal islands. It ranges from lowland regions to mountainous areas, at elevations of up to 2,440 metres above sea level, but typically occurs below 1,500 metres (1).
An efficient predator of small mammals, birds and lizards, the western diamond-backed rattlesnake hunts by ambush (4), laying in wait around burrows or runs (6). In addition to locating prey by sight and smell, this species also detects body-heat by means of heat-sensitive pits between the eyes and nostrils. When in range, prey is dispatched with a rapid strike, delivering a large quantity of highly toxic venom, which kills the animal within seconds (4). In addition to its toxic effects, the venom also has a role in digestion, and within 24 hours of the prey being ingested, the venom will have broken down the skin and begun to digest the internal organs (7). While the western diamond rattlesnake will usually attempt to escape from potential threats, when cornered, this species will give the characteristic warning rattle, raise its head and the anterior of its body, and may strike if further provoked (4). This species is active during the night in the summer, but extends its activity into the cooler times of day during the spring and autumn (7). During the winter the western diamond-backed rattlesnake undergoes a process analogous to hibernation in mammals, called brumation, in which the low environmental temperatures reduce the snake’s metabolic rate and limit its activity. During this time, the western diamond-backed rattlesnake may form large aggregations in upland areas, which shelter in dens located in abandoned mines, caves, or rock crevices (1) (7).
The western diamond-backed rattlesnake has two breeding periods, the first occurring in the spring, and the second in late summer/autumn. Sperm from the latter period may be stored in the female’s body throughout the winter before being used to fertilise the eggs (8). The western diamond-backed rattlesnake bears live young, and litters may number from 4 to 61 offspring (3). The newborn snakes are well-developed, and already equipped with fangs and toxic venom, but do not reach sexual maturity until three to four years old (4).
With a wide range and a relatively stable population exceeding 100,000 adults, there is little threat to the western diamond-backed rattlesnake at present. Nevertheless, severe regional declines have occurred as a result of habitat destruction, road traffic, hunting and persecution. Organised hunts known as “rattlesnake roundups” occur in some states, with the aim of ridding the area of rattlesnakes (1). The hunts have been criticised on the basis that they not only disrupt the ecosystem, by removing an important rodent predator, but also use methods that are environmentally destructive and impact non-target species (9).
While there are currently no known conservation measures specifically targeting the western diamond-backed rattlesnake, this species occurs in several protected areas throughout its range (1).
To learn more about the issues surrounding “rattlesnake roundups” visit:
- The Humane Society of the United States (September, 2009)
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- Moult: in snakes, a process of growth, in which the outer layer of the skin is shed allowing the body to become larger.
IUCN Red List (June, 2013)