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Western Diamond-backed Rattlesnake (Crotalus atrox)

[/vc_column_text][gap size=”12px” id=”” class=”” style=””][/vc_column][/vc_row][vc_row][vc_column width=”1/2″][vc_single_image image=”2156″ img_size=”large” alignment=”center” style=”vc_box_rounded”][vc_column_text]Photo by Roger Repp[/vc_column_text][/vc_column][vc_column width=”1/2″][vc_row_inner][vc_column_inner width=”1/2″][vc_single_image image=”2780″ img_size=”medium” alignment=”center” onclick=”img_link_large”][vc_column_text]Western Diamond-backed Rattlesnake in a Catclaw Acacia. Photo by Dan Bel[/vc_column_text][gap size=”12px” id=”” class=”” style=””][/vc_column_inner][vc_column_inner width=”1/2″][vc_single_image image=”2781″ img_size=”medium” alignment=”center” style=”vc_box_rounded” onclick=”img_link_large”][vc_column_text]Photo by Roger Repp[/vc_column_text][gap size=”12px” id=”” class=”” style=””][/vc_column_inner][/vc_row_inner][vc_row_inner][vc_column_inner width=”1/2″][vc_single_image image=”2782″ img_size=”medium” alignment=”center” style=”vc_box_rounded” onclick=”img_link_large”][vc_column_text]Photo by Roger Repp[/vc_column_text][gap size=”12px” id=”” class=”” style=””][/vc_column_inner][vc_column_inner width=”1/2″][vc_single_image image=”2783″ img_size=”medium” alignment=”center” style=”vc_box_rounded” onclick=”img_link_large”][vc_column_text]Male combat. Photo by Roger Repp[/vc_column_text][gap size=”12px” id=”” class=”” style=””][/vc_column_inner][/vc_row_inner][vc_row_inner][vc_column_inner width=”1/2″][vc_single_image image=”2784″ img_size=”medium” alignment=”center” style=”vc_box_rounded” onclick=”img_link_large”][vc_column_text]Cratering circle left by a coiled Western Diamond-backed Rattlesnake, Cochise County. Photo by Jim Rorabaugh[/vc_column_text][/vc_column_inner][vc_column_inner width=”1/2″][vc_single_image image=”2785″ img_size=”medium” alignment=”center” style=”vc_box_rounded” onclick=”img_link_large”][vc_column_text]Western Diamond-backed Rattlesnake eating Phainopepla, Cochise County. Photo by Jim Rorabaugh[/vc_column_text][/vc_column_inner][/vc_row_inner][vc_row_inner][vc_column_inner width=”1/2″][vc_single_image image=”2786″ img_size=”medium” alignment=”center” style=”vc_box_rounded” onclick=”img_link_large”][vc_column_text]Western Diamond-backed Rattlesnake. Photo by Young Cage[/vc_column_text][/vc_column_inner][vc_column_inner width=”1/2″][vc_single_image image=”2787″ img_size=”medium” alignment=”center” style=”vc_box_rounded” onclick=”img_link_large”][vc_column_text]Western Diamond-backed Rattlesnake eating road-kill mouse, Cochise Co., Photo by Jim Rorabaugh[/vc_column_text][/vc_column_inner][/vc_row_inner][vc_row_inner][vc_column_inner width=”1/2″][vc_single_image image=”2788″ img_size=”medium” alignment=”center” style=”vc_box_rounded” onclick=”img_link_large”][vc_column_text]Western Diamond-backed Rattlesnakes: courtship. Pima Co. Photo by Roger Repp[/vc_column_text][/vc_column_inner][vc_column_inner width=”1/2″][vc_single_image image=”2789″ img_size=”medium” alignment=”center” style=”vc_box_rounded” onclick=”img_link_large”][vc_column_text]Western Diamond-backed Rattlesnake with scavenged mouse (complete with maggots). Pinal County, AZ. Photo by Marty Feldner[/vc_column_text][/vc_column_inner][/vc_row_inner][vc_row_inner][vc_column_inner width=”1/2″][vc_single_image image=”2790″ img_size=”medium” alignment=”center” style=”vc_box_rounded” onclick=”img_link_large”][vc_column_text]Western Diamond-backed Rattlesnake, Photo by Young Cage[/vc_column_text][/vc_column_inner][vc_column_inner width=”1/2″][vc_single_image image=”2791″ img_size=”medium” alignment=”center” style=”vc_box_rounded” onclick=”img_link_large”][vc_column_text]Western Diamond-backed Rattlesnake, Photo by Young Cage[/vc_column_text][/vc_column_inner][/vc_row_inner][vc_row_inner][vc_column_inner width=”1/2″][vc_single_image image=”2792″ img_size=”medium” alignment=”center” style=”vc_box_rounded” onclick=”img_link_large”][vc_column_text]Western Diamond-backed Rattlesnake, Photo by Young Cage[/vc_column_text][/vc_column_inner][vc_column_inner width=”1/2″][vc_single_image image=”2793″ img_size=”medium” alignment=”center” style=”vc_box_rounded” onclick=”img_link_large”][vc_column_text]Western Diamond-backed Rattlesnake. Note the 5 small scales between the supraocular scales (see Mohave Rattlesnake account for comparison). Photo by Young Cage[/vc_column_text][/vc_column_inner][/vc_row_inner][/vc_column][/vc_row][vc_row][vc_column width=”1/6″][/vc_column][vc_column width=”2/3″][vc_column_text]

Description

Crotalus atrox is a member of the lineages Viperidae (vipers) and Crotalinae (pit vipers). Thick in body and impressive in length, it is the second largest rattlesnake to be found in the United States. Dubious size of over 210 cm (seven feet) and mass of 6.5 kilograms (14 pounds) have been reported in the eastern part of its range, but within the 100 mile circle, anything over 140 cm, and/or one kilogram would be a remarkable specimen. The adult females under our watch average 80 to 90 cm, the males an even 100 cm, with mass averaging 350 and 450 grams respectively.

This wide-ranging species occurs from western Arkansas, west to Oklahoma, south through central Texas, and westward to Southern California, and southward again to central Mexico. In Arizona, an imaginary line drawn from Lake Mead across the southern edge of the Mogollon Rim would roughly encompass its range.

The vast area that this species occupies causes any form of general description to become a formidable task. It can be found anywhere from sand dunes at near sea level to grasslands and oak juniper woodlands at over 2000 meters (6000 feet). As such, it is a habitat generalist that adapts to many variables within its environment.

Its coloration shows considerable variability. The dorsal base coloration can range anywhere from light silver with dark gray blotches to a light tan with darker brown blotches. Its blotches are outlined by dashed white lines, sometimes forming the shape of a diamond—which has earned this snake its name. At least locally, C. atrox can individually change its coloration to match the above description, going from brownish hues when cold to grayish hues when warm. Its triangular-shaped head has a pale band that arcs from nostril to upper labials, with a similar but narrower band behind the eye. The ventral coloration runs from cream to dull yellow. The tail is symmetrically encircled with white and black bands of near-equal width, and, of course, ends with a rattle.

As with all members of Viperidae, C. atrox is equipped with needle sharp fangs with which to envenomate its prey—or would-be predators. The fangs fold against the roof of the mouth when not in operation, and both swing and flare outward when the snake delivers a strike. The large size of this species equates to large volumes of venom being injected from glands on either side of the head through the hypodermic needle-like fangs. In the United States, this species is responsible for more venomous snake bites than any other snake. Prey items are mainly, but not limited to, small rodents, rabbits, and lizards. These are actively hunted day or night, (depending on season and weather factors), by utilizing its extraordinary sense of smell to locate the vicinity of fresh prey. It then coils in close proximity to the desired area in ambush posture, and waits for the hapless victim to wander within striking range. Like all members of the pit viper family, C. atrox has yet another offensive weapon—two heat-seeking cavities between nostril and eye that detect prey items as “hot spots” in the night.

Within the 100 Mile Circle, a personal 13-year study has revealed that C. atrox is not only the most common rattlesnake encountered—it is the most common snake period. Of over thirty types of snakes found in random acts of searching, 40% have consistently been C. atrox. The preliminary hypotheses related to this phenomenon are: bimodal mating seasons, (late August to early October, March through April); large size; tolerance to both cold and hot conditions; maximum habitat utilization (finding warm hibernacula); ability of females to store sperm for long periods of time; live bearing; maternal accompaniment of young, venomous; long lived (15 years plus); and complex social structure.

In our area, two independent and ongoing studies (Emily Taylor and Dale DeNardo, and Gordon Schuett and Roger Repp) have discovered that young are born early to late August, and tend to be in smaller clutches than might be recorded elsewhere. (2-7, 3-8, 4.4 and 4.6 average respectively). The more commonly quoted figure of 10 to 20 young may transpire in wetter parts of its range, or exceptional years when weather factors are perfect. There is much work to be done along the lines of reproduction, but evidence is mounting that females skip a year or more between birthing events. Fat, healthy females seem to attract mates, and body fat may play a key role in triggering follicular growth.

The wide range this species occupies assures its survival well into the next century. But as Tucson begins to expand ever outward, trends reveal that increasing numbers of road kills versus live snakes are being encountered. Once humans settle into any given area in number, C. atrox eventually lose yet another portion of its range.

Authors: Roger A. Repp and Gordon W. Schuett
Originally published in the Sonoran Herpetologist “Herpetofauna of the 100-mile Circle” 15 (12) 2002

For additional information on this species, please see the following volumes and pages in the Sonoran Herpetologist: 1995 Nov:112-121; 1996 May:46-47; 1997 Apr:38-44; 1998 Feb:16-18; 1998 Apr:40-42; 2001 Jun:62-63; 2005 Dec:138; 2006 Aug:86-90; 2006 Nov:128; 2011 Sep:86-87; 2011 Nov:114-116; 2012 Sep:88-89; 2016 Dec:53-56; 2017 Dec:72-80.

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