PACIFIC RATTLESNAKE. Crotalus oreganus Holbrook

Field characters.—A segmented horny 'rattle' at end of tail (fig. 64). Body stout; tail (vent to rattles) short, usually less than 1/10 length of body (to vent). Head bluntly triangular; a definite constriction at neck. (See pl. 59b.) Scales on back relatively large, keeled, and in 23 to 27 rows. Total length (snout to end of rattles) up to 4 feet (possibly more); girth of body up to 5 inches. General coloration yellowish brown or grayish brown, with a series of large saddle-marks of dark brown or black along middle of back; also two rows of smaller dark spots along each side of body, these alternating in position with the large blotches. Track: Broad, much curved; on soft roadways shows much earth pushed up at sides of curves (pl. 40b).

Occurrence.—Resident in numbers on west slope of Yosemite region where recorded from Snelling eastward to altitude of 8100 feet near junction of Sunrise and Merced Lake trails. Lives chiefly near rocks and in brushy places, but also in open country of lowlands.

The Pacific Rattlesnake is the only poisonous animal to be found among the vertebrates in the Yosemite section, and the experience of the great numbers of visitors to the region has shown that there is little real danger from even this animal. 'Rattlers' are to be found from the plains of the San Joaquin Valley eastward into the mountains to an altitude of 8100 feet, though they are more common in the foothill country than at the higher levels. Yosemite Valley originally had a fairly large population of rattlesnakes, but these reptiles have been pretty well eliminated there, by the hand of man, within the past two decades. On the east slope of the Sierras, between the Yosemite region and the neighborhood of Lake Tahoe, rattlesnakes appear to be wanting entirely, though they are present farther east in the Great Basin territory.

The danger from rattlesnakes is often exaggerated. This is not to say that their bite is not poisonous, for that has been proved beyond doubt. But the rattlesnake is ordinarily not an aggressive animal and when met with will usually try to escape if not cornered. Very few persons are actually bitten and of those who are bitten but a small percentage succumb, as in most cases prompt application of proper treatment counteracts the effect of the poison.

The extreme size attained by the Pacific Rattlesnake in the Yosemite region is not known with certainty. Exact measurements of freshly killed individuals are scarce. Occasionally rattlers measuring as much as 5 feet from tip to tip are killed in the foothill country, according to Mr. Donald D. McLean. The largest example obtained by our party measured 36 inches (915 mm.) in length. The average length of the rattlers in the region is probably slightly under this. Measurements from skins, either fresh or dried, are of but little service save to indicate the general size of the snakes from which they were taken. Such skins may be, and often are, stretched from 10 to 25 per cent beyond the dimensions of the reptile 'in the flesh.'

The head of the rattlesnake is bluntly triangular in outline and sharply set off by the relatively slender neck (pl. 59b). This shape of head, though always to be found in the rattler, is not a reliable character for distinguishing poisonous snakes generally from harmless ones. The garter and gopher snakes, both harmless species, are able to assume this form of head temporarily. The head of the rattlesnake shows other distinctive features: the upper surface is devoid of large plates, being covered with small scales; there is a distinct pit between the nostril and the eye; and the pupil of the eye is vertically elliptical. The body of the rattlesnake is usually thick, perhaps 5 inches in circumference in a large example. The scales on the body of the snake are large and coarse and each scale is surmounted by a conspicuous lengthwise ridge or keel. The tail is quite short and bears at the end the dry resonant rattle which has given rise to the common name of the reptile. The coloration of rattlesnakes is apt to be quite variable, even in a single locality. Some individuals may be dark, even nearly black, while others are extensively gray, reddish, or yellowish.

The rattle of the rattlesnake is a structure which is formed incidentally to the general molt of the outer skin. (See fig. 64). Snakes of all species cast off the outer, worn layer of the skin one or more times each year. In the garter or gopher snakes, in which the tail is tapered to the end, the 'slough' usually comes away in a single piece, being turned inside out as the snake glides out of it, and such cast skins are to be found from time to time in the field. The molt of the rattlesnake, so far as the body is concerned, is the same as in other snakes. But the tip of the tall in this species is blunt and bears a thickened horny covering with one (later two) constrictions. When the molt occurs, this horny tip is held by the new tip growing beneath it. Successive molts result in a series of these dry segments being formed, each of which is caught over or under the two adjacent ones. The number of segments in a rattle (provided the first small segment or 'button' is still adhering) thus indicates merely the number of times the snake has molted. Large snakes have been found in which only a few segments of the rattle remained, the balance having been worn or broken off. The largest number of rattles which we know definitely to have been found on a rattlesnake was 22. Most individuals have 8 to 10.

Fig. 64. Rattle of Pacific Rattlesnake (a) and diagrammatic section of same (b), showing manner in which parts of rattle are held together and yet remain loose enough to permit of movement when tail is vibrated.

When excited the rattlesnake vibrates the tip of the tail rapidly, causing the horny rattle to give forth an insistent cicada-like buzz that is usually recognizable at once. If danger threatens, the snake places its body in a series of S-shaped curves, the tip of the tail being held vertically. To "strike," the reptile straightens out suddenly, lunging at its prey or enemy, dropping the lower jaw and erecting the hollow teeth or 'fangs' in the roof of the mouth so that they point almost straight forward. (See fig. 65.) At best, the rattler cannot strike more than two-thirds its total length; one-third is probably the average distance struck. Stories of snakes "jumping" at their enemies are gross exaggerations. If the snake hits the object of its attack the two hollow fangs are buried in the flesh, the lower jaw is brought up and the poison is forced into the wounds. Leather tramping boots or puttees are likely to afford full protection against the rattlesnake, as the animal is not known to strike to a height of much if any over 12 inches above the ground.

Fig. 65. Sketch of head of Pacific Rattlesnake, showing important parts of the anatomy which function in the bite and poisoning by this snake. The action of the poison apparatus is as follows. As the snake moves its head forward to strike a victim, be it man or animal, Muscle 1 (spheno-pterygoid) is contracted. This pushes forward the tooth-bearing home preceding it and this in turn rocks forward the bone which carries the fang and causes the fang to come in line with the strike of the head. After the fang has entered the body of the victim, Muscle 1 relaxes and Muscles 2 and 3 (external pterygoid and spheno-palatine) contract, drawing the fang more deeply into the flesh. Then Muscle 4 (anterior temporal) contracts, bringing up the lower jaw and at the same time compressing the poison gland so that the poison is forced along the duct, through the fang, and into the flesh of the victim. Then the whole musculature of the head and neck relaxes, the head and fangs are drawn away from the victim and the fang is depressed again. This whole series of actions occupies but an instant. The fang is shown partly elevated. Normally it lies close to the roof of the mouth and is covered by a membrane not shown in the drawing. When the fang is erected, preparatory to biting, this membrane is folded down at the base of the fang and directs the poison as it leaves the end of the duct of the gland into the base of the fang. (Adapted from Noguchi.)

If a person chances to be struck by a rattler certain things should be done promptly, but with as little flurry as possible.

1. If bitten on the leg or arm, apply a tourniquet above the wound, that is, toward the heart from the bite. This is done in order to stop the flow of blood toward the heart and prevent the poison from getting into the general circulation. A bandana handkerchief with two opposite corners knotted together, slipped over the limb and twisted tight by means of a stick makes a good tourniquet.

2. Cut open the site of the punctures with a pocketknife so as to promote a flow of blood and thus tend to wash out the poison. If available, inject potassium permanganate solution into the area immediately surrounding the bite. If the solution cannot be made or injected apply a few crystals of permanganate directly at the place of the bite.

3. After about half an hour loosen the tourniquet slightly for a fraction of a minute and then tighten it down again. Thereafter, loosening and tightening should be done every fifteen minutes or so. This is to allow the poison remaining in the wound to be absorbed by the system gradually and also to prevent gangrene setting in about the bite because of impeded circulation.

4. The patient should be placed in a comfortable position as soon as possible, and kept quiet. A mild stimulant such as coffee may be administered. Do not give whiskey or brandy. A doctor should be summoned as soon as possible.

For the rattlesnake the venom serves a twofold purpose, to kill animals which the snake uses for food, and to protect the reptile against its enemies. The food of the rattlesnake consists largely of small rodents of which locally, chipmunks form a considerable part. These are killed by the snake's poison and then swallowed. A rattler killed on Smith Creek, 6 miles east of Coulterville, July 21, 1920, had the remains of a Mariposa Chipmnnk in its alimentary canal, only the hind legs and tail remaining undigested. Another snake found on the Snow Creek zigzags of the trail to Tenaya Lake on September 29, 1915, had an adult Long-eared Chipmunk in its throat, with the tail protruding from the reptile's mouth. In both of these instances the snake had swallowed its prey head foremost. But a case has been reported by Dr. Barton W. Evermann (1915b) in which a rattlesnake killed near Cascade Falls (west of the lower end of Yosemite Valley) on July 15, 1914, contained an adult Mariposa Chipmunk which it had swallowed tail first! "The head of the chipmunk was toward the snake's head, and its legs, tail and fur all lay back toward the snake's tall, smooth and in perfect order."

A strong belief in many places is that the rattlesnakes "go blind" in late summer and are then very dangerous and likely to strike without warning. The basis of fact underlying this notion is that many of these snakes molt in that season, and that for a time just before the molt the skin overlying the eyes, which is likewise sloughed off, is clouded by the secretion which loosens the outer skin preparatory to its removal. Another widespread notion is that rattlers go about in pairs; we have never been able to find any conclusive evidence on this point.

The temperament of the rattlesnake is quite different from that of the racers, and reflects in a way the differences in form between the two types. The rattlesnake is generally quiet and slow, even lethargic, and is wont to spend much of its time in some warm sunny spot, as on a rocky outcrop. In such a place, too, it waits for prey. The cleared area of a trail is often made use of as a sunning place and this accounts for the number of rattlers encountered by hikers. If come upon, on trail or rocks, a rattlesnake may remain quiet, or again it may endeavor to glide away. Only when it is cornered, or when it 'thinks' itself cornered, is the rattler likely to prepare for striking.

In the winter months rattlesnakes "den up," that is, go into dormancy in holes in the ground and sometimes in crevices in rocks. In certain places, ground squirrel burrows are used. In a few localities regular dens have been reported where large numbers of these snakes are said to congregate together for the winter season. One such den is reported to have been found in the neighborhood of Horseshoe Bend when the Yosemite Valley Railroad was being constructed previous to 1908. Another is said to have been blown up in Hetch Hetchy Valley incidental to work on the San Francisco water project. We have no personal knowledge of occurrences of this nature.