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Western Diamond Rattlesnake
Colouration.—The pattern is very similar to that of the preceding and allied species, but the ground-colour is different as is the tail, which is white, with jet-black rings.
Dimensions.—Occasional specimens six feet in length are taken, and sometimes, though very rarely, seven-foot specimens are recorded. All of the records for these very large specimens seem to come from Texas. Records from various localities prove interesting condition regarding dimensions, for there appear to be several races of the species, some dwarfed and seldom growing to a length of four feet; others averaging a length of five feet with quite slender bodies; while from some localities all of the snakes develop to a considerable size and are more thick-set than the former reptiles. From several dozen Texas specimens an average has been figured, and follows:
Distribution.—The species occurs principally in the sub-arid and desert regions of Texas and the Southwest. It is found commonly in central and western Texas, southern New Mexico, Arizona and southern California. Although it may be said to be most abundant in Texas where it occurs over a large area, it is the most common rattlesnake of the genus throughout the entire range. Its habitat extends well into the Tableland of Mexico, but in this part of the range a peculiar phase of colouring and scutellation of the head, is treated in a succeeding description.
Habits.—Like the Southeastern Diamond-back Rattlesnake, this is a nervous and irritable serpent, but as a captive is more hardy. It will take rats, rabbits, guinea pigs and birds. An example seventy-three inches in length has lived in the reptile house of the New York Zoological Park for over four years. The snake is given a half-grown rabbit regularly, every week. Unless preparing to shed its skin it never refuses the morsel. When the snake arrived from Texas, it was particularly vicious for one of its species, literally hurling the body into a coil and striking repeatedly at its keeper--and it has remained so. In spite of the four years' attention Keeper Snyder has given it, in the cleaning of the cage and presenting the food, the creature strikes immediately as the door is slid back. A step in the passageway behind the cages causes this dangerous brute to rattle nervously, shift its coils and inflate the body for combat. On three occasions a companion of the same species was placed in the cage, and this in each instance resulted in the original occupant refusing to feed. Upon the third trial it stubbornly fasted for six weeks, when the offending serpent was removed. The big rattlesnake took its rabbit two days after.
Habits.—Seems to be essentially a mountain reptile. All of the Tucson specimens were taken at an elevation, some of them on ledges in company with the black-tailed rattlesnake. Crotalus molossus. The typical form of atrox was common in that vicinity, but always in the desert.
Next to the diamond-back rattlesnake of the southeastern United States, this is the largest species of the genus. It attains a length of seven feet.
The ground-colour may be yellowish gray, pale, bluish gray or pinkish, according to locality; the pale borders of the diamond markings are dull white. Compared with the rich, olive and yellow tints of the Eastern species, the present reptile evinces a dull and faded pattern.
The most showy individuals are from the desert regions of Arizona. The ground-colour is distinctly pinkish, the borders of the rhombs vividly outlined in white; the tail chalky white with jet-black rings.
On all specimens the head markings are similar to the allied species, but the pale stripes on the side of the head are not so vividly defined.
Total Length . . . . . 4 feet, 6 inches.
Tail, without rattle . . . . . 3 3/4 inches.
Diameter of Body . . . . . 2 1/4 inches.
Width of Head . . . . . 1 7/8 inches.
Length of Head . . . . . 2 1/8 inches.
Length of Rattle, 10 segments . . . . . 2 1/4 inches.
(Mexican Phase of Crotalus atrox)
On the Mexican Tableland, which extends into southern Arizona, is a peculiar phase of Crotalus atrox that might be confused with a more westerly species--Crotalus oregonus--owing to the diamond markings (on most specimens) being rather blunt and well separated--not forming a connected chain. Such examples are yellowish or greenish, and the black and white bars on the tail are dull and broken. These snakes appear quite different from the powdery gray form, with the vividly marked black and white tail, of the sub-arid plains and the deserts. The head markings resemble Crotalus oregonus, owing to their definition and the breadth of the forward bar. Such specimens have the forward portion of the head covered with irregular plates, but no two examples show this character to be exactly alike.