Western Diamond-backed Rattlesnake (Crotalus atrox)

— This article by Jerry Cates, first published on 9 February 2010, was last revised on 23 April 2016. © Bugsinthenews Vol. 11:02(05).

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Viperidae: Crotalus atrox, Western Diamond-backed Rattlesnake, Sweetwater, TX 03.12.10

The Western Diamond-backed Rattlesnake (Crotalus atrox, Baird & Girard, 1853) is an animal (kingdom Animalia) with a hollow, dorsal nerve cord (phylum Chordata), a backbone (subphylum Vertebrata), and jaws (infraorder Gnathostomata). It is a descendent of  four-footed ancestors (superclass Tetrapoda), has a terrestrially-adapted egg (an Amniote), breathes air and is ectothermic, i.e., cold-blooded  (class Reptilia). It has a scaly skin (order Squamata), is without legs, eyelids or external ears (suborder Serpentes), possesses relatively long, hinged, hollow fangs to inject venom (family Viperidae), a heat-sensing pit organ between the eye and nostril (subfamily Crotalinae), and a rattle on the end of its tail (genus Crotalus).

All serpents in the genus Crotalus (which embraces all the rattlesnakes) are native Americans, and are distributed from southern Canada to northern Argentina. Crotalus atrox (L. atrox: “fierce, terrible, frightening”) is distributed throughout the southwestern United States, from east Texas and east Oklahoma, westward through the Texas panhandle into south and southeastern New Mexico,  south Arizona, and southeastern California, then south, into portions of northwestern and northeastern Mexico.

Western Diamond-backed Rattlesnake (Crotalus atrox), 040110, San Antonio, Texas–Lateral Head, with Fangs Extended

Slightly smaller than the eastern diamond-backed rattlesnake (Crotalus adamanteus), the western diamond-backed rattlesnake’s record length is approx. 7 feet. Due to aggresive control efforts over the past century, however, this species rarely exceeds 4 feet in length today except in sparsely inhabited areas where they are able to exist in relative security, unmolested by man or the snake’s natural predators.

This species has a background coloration that is usually a dusty gray-brown, but varies, and can be chalky white, pinkish, pinkish brown, dark red, yellow, or shades of orange. The background coloration is typically, but not always, broken by a series of 24-25 dorsal spinal blotches, normally dark gray, gray-brown, or brown in color. These blotches begin at the neck, usually forming squares or rectangules. These morph, down the spine, first to hexagonal then–along most of the midbody spine–to diamond-shaped blotches; these are usually thinly bordered in a checkered dark brown anteriorly and more broadly in a jagged chalky white posteriorly, much as the designs sometimes seen on native American blankets.

As the blotches continue toward the tail, they morph again , elongating laterally, and truncating longitudinally, losing their distinctive borders in the process. Finally, the last few inches of the tail is distinctively marked in alternating black and white bands, the black bands 2-8, but usually 4-6, in number, with the black bands serving as demarcations for the snake’s “coon tail” so that the white bands usually number one less than the black ones.

Western Diamond-backed Rattlesnake (Crotalus atrox) juvenile, 040110, San Antonio, Texas: Martha–Tail, with Rattles

Where the “coon tail” bands join mid-dorsally, it is common for the white bands on one side of the body to join with black bands on the other side, along the length of the tail, giving an even more striking appearance. In fact, the appearance is strongly suggestive of the Sillitoe tartan design on hatbands worn by police in the U.K, Australia, New Zealand, and by patrol officers of the Chicago, Ill. police department to designate their personnel as armed members of the emergency services. It might be gathered, from this fact, that similar markings on this rattlesnake’s tail would enhance its faculty for warning large animals to stay clear. This visual warning is given added credulity by the ominous sound of the snake’s rattle.

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