This is a “northern black tailed” rattlesnake, Crotalus molossus molossus. It’s range includes portions of southern and central Arizona, southern New Mexico and southwestern Texas and adjacent Mexico (Connant 1975). In the eastern aspect of its range, it inhabits the wooded canyons, cliffs and rock piles in the west-central Edwards Plateau, and the adjacent Chihuahuan Desert. Though present only in the southwestern extreme of the hurricane prone region of North America (Tennant, 1998), it is of importance to those living in these regions, and first-responders offering aid to those affected by such a disaster.
Typically a mild tempered rattlesnake, it still packs moderate, to large amounts of potent venom. Because of apparent antigenic differences in black tailed rattlesnake venom, treating bites with “CroFab” antivenin can require comparatively larger doses than bites of other rattlesnake species (Consroe et al., 1995; Sanchez et al 2003a, 2003b; Yarema and Curry, 2005).
The ground color of this species predictably varies across its US range from light-gray (Texas), to yellowish-green (Arizona). The dorsal patterning consists of a series of black diamond-shaped blotches with light centers. Posterior to the neck region, the lateral points of each diamond typically extend ventrally, forming a series of distinctive crossbands. On the posterior 2/3rds of the body, the markings are reduced to light centered cross bands. The tail of this species is typically solid black but, unlike the timber rattlesnake, the black coloration does not extend anterior to the vent. The head bears a prominent solid black stripe that extends diagonally across its lateral aspects, from an area just above the corners of the mouth, crossing the anterior crown, thereby creating a mask-like marking that effectively conceals the eyes (Tennant, 1998).
This image was provided by the Centers for Disease Control and Prevention/Edward J. Wozniak D.V.M., Ph.D./Christina Wozniak at the Houston Zoo. [0003-0702-0313-1926] by 0003