GARTER SNAKES. Genus Thamnophis⁴²

Field characters.—Body long, slender and tapering; tail pointed; scales of back all ridged (keeled), never in more than 23 rows. (See fig. 62b.) Coloration of upper surface black or grayish, with a light line along each side of body and another line down middle of back, or else many small light spots on back; pattern never in large blotches or cross-bands; under surface bluish green. Emit a foul-smelling liquid when handled.

Occurrence.—Common along streams, about margins of ponds, and in wet meadows throughout the Yosemite region up at least to 8600 feet altitude.⁴² Live on damp ground and in water. Several individuals often found together.

---

⁴²The identification of the species and subspecies of Garter Snakes is often a difficult matter even for a trained herpetologist. There is much variation among individuals, especially in the numbers of scales; consequently series of specimens are usually required to properly identify the snakes from any one locality. Difficulty may be experienced in attempting to name certain individual specimens. The latest comprehensive study of the Garter Snakes of western North America is that by Van Denburgh and Slevin (Proc. Calif. Acad. Sci., ser. 4, vol. 8, 1918, pp. 181-270, pls. 7-17) who have identified our specimens from the Yosemite region as belonging to two species, one of which is represented by three subspecies. These forms, with their principal characters (as exhibited by the most typical specimens), and the localities at which they were found, are as follows:

PACIFIC GARTER SNAKE, Thamnophis sirtalis infernalis (Blainville), has (usually) 7 scales on upper lip (supralabials), not more than 19 lengthwise rows of scales on back, and upper surface black with three distinct light stripes, one down middle of back and another low on each side of body. It is a lowland species, common at Snelling and Lagrange and ranging eastward as far as floor of Yosemite Valley.

GIANT GARTER SNAKE, Thamnophis ordinoides couchii (Kennicott), has usually 8 scales on upper lip, usually 21 rows of scales on forepart of body, and upper surface of body black but with no light line down middle of back, the upper surface being marked with small scattered light spots. (See fig. 62b.) It is a central California race, found on meadows in Yosemite Valley.

MOUNTAIN GARTER SNAKE, Thamnophis ordinoides elegans (Baird and Girard), has (usually) 8 scales on upper lip, not often more than 19 rows of scales on back, and a dark body coloration with 3 distinct light stripes, one down middle of back and one on each side of body. It is a high mountain subspecies, reported from floor of Yosemite Valley, but more common in the higher altitudes as at Merced Lake (7500 feet) and Tuolumne Meadows (8600 feet).

WANDERING GARTER SNAKE, Thamnophis ordinoides vagrans (Baird and Girard), has (usually) 8 scales on upper lip, 21 rows of scales on forepart of body, and a dull (often grayish or greenish) body coloration, but with a distinct line down middle of back; large scales on under surface often with black markings. This snake is a Great Basin form, taken at Walker Lake and near Mono Lake.

---

The Garter Snakes are often called Water Snakes in recognition of their association with streams, ponds, and wet meadows, and through most of the Yosemite region they may be looked for confidently in such surroundings. They occur the most widely of all the snakes in the region. Moreover, they are often found in considerable numbers in a single locality; hence, the Garter Snake population, as a whole, is far above that of any of the other snakes, or, perhaps, of all other snakes put together.

Fig. 62. (a) Western Yellow-bellied Racer; Yosemite Valley, June 4, 1915. (b) Giant Garter Snake; Yosemite Valley, May 22, 1919. Both photographed from freshly taken specimens, about 2/5 natural size.

In hand or at close range the Garter Snakes may be readily distinguished from all other snakes of the Yosemite region by the fact that they possess keels or ridges on the scales of the back, in combination with a pattern of coloration which never consists of large blotches. The most usual color pattern among the Garter Snakes is a dark upper surface with a light stripe down the middle of the back and another similar stripe low on each side of the body. The Giant Garter Snake is an exception, as it has only a short stripe on the neck region and the rest of its body is flecked with small spots of light color. The California Striped Racer of the foothill oaks and chaparral has a long slender body and a dark upper surface with a stripe along each side but not in the middle. This snake looks at first glance somewhat like a garter snake, but all of its scales are smooth and it has no light line down the middle of the back. The rattlesnake and gopher snake both have keeled scales, but the patterns of coloration and bodily form in these species are entirely different from those of the garter snakes.

The favorite haunt of the garter snakes is the margin of a shallow pool with gently sloping shores and bottom, a pool bordered closely by a dense stand of grass or other low plants. In such places these snakes often abound. Five were noted close together on the shore of one small pond near Tuolumne Meadows on July 6, 1915, and greater numbers have been seen in other localities. Such a place gives the snakes an easy retreat into the grass on one side and into the water on the other, while food in the form of frogs, tadpoles, or small fishes is usually to be obtained close by. When undisturbed the snakes will spend much of the day in sunning themselves on the shores of such a pool.

When it takes to water a garter snake swims readily, with only its head above the surface, making progress by whipping the body from side to side in broad loops. At best its speed is slow, not to be compared with that of any of the fishes, and after going a short distance it will usually rest momentarily before resuming its course. When resting in shallow water it will allow its body to sink to the bottom and will hold only its head above the surface; but in a deeper stream or pool it will glide up to the margin and rest its chin on a projecting ledge or log. On land as well as in water these snakes are slow movers, that is, for snakes. The form of the scales on the under surface of their bodies, and the musculature by which the free edges of these scales are lifted, do not seem to be adapted for rapid travel such as is exhibited by the racers. The garter snakes make their best progress when in a meadow, for there the scales get more of a purchase on the irregularities of the grass and sod.

The garter snakes are not belligerent, rarely if ever will they 'show fight' as do gopher snakes or rattlers. Even when harried they usually try to slip quietly off into the grass or swim away in the water. If captured, a garter snake will as a rule pour out a malodorous liquid that is effective in procuring its release, especially if its captor be a human being. How much of a protection from wild enemies this odor affords, is not known.

Garter snakes have large litters of young. Rarely are there less than 10 or a dozen, and litters of 20 and more are not uncommon. The rapidity of its reproduction probably reflects the degree of danger to which these reptiles are exposed. The eggs of Garter Snakes are not deposited on land and left to hatch unattended, as are those of many snakes, but are retained in the body of the female and developed there, and the young are born alive.

These snakes do not usually have to go far from their favorite haunts to find food, as they feed to a large extent on frogs, toads, tadpoles, and small fishes. The relative scarcity of frogs in certain meadows and along some of the slower moving streams, and their unusual abundance in some of the highest mountain lakes and along the swifter creeks, may perhaps be related to the presence or absence of garter snakes in these respective localities. Although 'cold-blooded' animals form the greater portion of the food of these snakes, they are not averse to taking birds or mammals when occasion offers. At Mono Lake Post Office on May 30, 1916, a Wandering Garter Snake was found trying to swallow a barely fledged young Modoc Song Sparrow. Both of the parent birds were highly excited and flew at the snake repeatedly.

The garter snakes, even in the lowlands, are seen but little during the colder portions of the year, while at the higher altitudes they spend several months in continuous hibernation. At Walker Lake a Wandering Garter Snake was picked up at 9 o'clock on the morning of September 13, 1915. It was some distance from water and so cold and torpid that it made practically no effort to escape. It would probably soon have gone into winter quarters in some sheltered crevice in the rocks. Tracks of a garter snake were seen near Snow Flat on October 5, 1915, but no evidence of activity was obtained after that date anywhere in the Yosemite region. By the third week of May, 1919, garter snakes were becoming active in Yosemite Valley. One seen wriggling across a road, May 21, near the Valley wall and going toward the river meadows, may have only just emerged from hibernation.