Common Garter Snake
Thamnophis sirtalis
Description 18-51 5/8" (45.7-131.1 cm). Most widely distributed snake in North America. Coloration highly variable, but back and side stripes usually well-defined. Side stripe confined to 2nd and 3rd scale rows (except Texas). Red blotches or a double row of alternating
black spots often present between stripes. Usually 7 upper lip scales. Scales keeled, in 19 rows. Anal plate single.
Endangered Status The San Francisco Garter Snake, a subspecies of the Common Garter Snake, is on the U.S.
Endangered Species List. It is classified as endangered in California. One of North America's loveliest snakes, this subspecies has suffered as its habitat, in San Mateo County, has been consumed by urban growth.
Subspecies Eastern (T. s. sirtalis), stripes normally yellow, occasionally brownish, greenish, or bluish, double row of alternating spots usually between stripes; some specimens lack stripes, some are all black, others with red between dorsal scales; s. Ontario, e. Minnesota, e. Iowa, e. and s. Missouri, Arkansas, and e. Texas to Atlantic coast from s. Newfoundland to s. Florida.
Texas (T. s. annectens), broad orange back stripe, side stripes on scale row 3 and on half of rows 2 and 4; Texas-Oklahoma border south through ec. Texas; isolated population in Texas panhandle.
Red-spotted (T. s. concinnus), black with well-defined narrow back stripe, black pigment extends onto belly, top of head red; nw. Oregon and extreme sw. Washington.
Valley (T. s. fitchi), brown or dark gray with well-defined back stripe, top of head black; c. and n. California (except area noted for California Red-sided), nw. Nevada, sw. and e. Oregon, Idaho, nc. Utah, w. Montana, and Washington east of the Cascades through British Columbia to se. Alaska.
California Red-sided (T. s. infernalis), resembles Red-sided, red blotches on sides, side stripe indistinct, top of head red; coastal California, Humboldt County to San Diego County.
New Mexico (T. s. dorsalis), resembles Red-sided but red markings between back and side stripes reduced and largely confined to skin between scales; Rio Grande Valley, extreme s. Colorado through New Mexico to extreme w. Texas.
Maritime (T. s. pallidulus), resembles Eastern, but back stripe faint or absent and spotting is well developed; status and range not resolved; Canadian Maritime provinces, Quebec, adjacent areas of New England.
Red-sided (T. s. parietalis), red or orange bars between back and side stripes variable, top of head olive; ec. and se. British Columbia, Alberta, and adjacent extreme sc. MacKenzie, c. Saskatchewan and s. Manitoba south through Great Plains to Oklahoma-Texas border.
Puget Sound (T. s. pickeringii), resembles Red-spotted, except back stripe largely confined to 1 scale row instead of 2 and top of head dark; Vancouver Island, adjacent coastal sw. British Columbia and w. Washington.
Chicago (T. s. semifasciatus), black vertical bars break side stripes in neck region, ne. and nc. Illinois, se. Wisconsin, and extreme nw. Indiana.
Blue-striped (T. s. similis), dark brown with dull yellowish or tan back stripe and bluish side stripes on 2nd and 3rd scale rows; nw. peninsular Florida, Wakulla County to Withlacoochee River.
San Francisco (T. s. tetrataenia), red markings between back and side stripes form continuous stripe, belly greenish-blue, top of head red; San Mateo County, California.
Breeding Live-bearing. Mates mostly late March to early May, occasionally in fall. 7-85 young born late June to August, earlier in Florida, to early October in the North. Young are 5-9" (13-23 cm) long; mature in 2 years.
Habitat Near water - wet meadows, marshes, prairie swales, irrigation and drainage ditches, damp woodland, farms, parks; sea level to 8,000' (2,450 m).
Range Atlantic to Pacific coasts; except desert regions of Southwest.
Discussion The most commonly encountered snake in many parts of its range. Active during the day and most frequently seen amid moist vegetation where it searches for frogs, toads, salamanders, and earthworms. Occasionally it takes small fish and mice. This species is able to tolerate cold weather and may be active all year in the southerly part of its range. It hibernates in great numbers in community dens in northerly range. Ill-tempered when first captured, it will bite or expel musk, but it tames quickly and soon becomes docile. Record longevity is 10 years.
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