Common Garter Snake

The common garter snake (Thamnophis sirtalis) is a species of snake in the subfamily Natricinae of the family Colubridae. The species is indigenous to North America and found widely across the continent. There are several recognized subspecies. Most common garter snakes have a pattern of yellow stripes on a black, brown or green background, and their average total length (including tail) is about 55 cm (22 in), with a maximum total length of about 137 cm (54 in). The average body mass is 150 g (5.3 oz). The common garter snake is the state reptile of Massachusetts.

Taxonomy and etymology

The subspecific name fitchi is in honor of the American herpetologist Henry Sheldon Fitch.

The subspecific name pickeringii is in honor of the American naturalist Charles E. Pickering.

Subspecies

Current scientific classification recognizes 12 subspecies (ordered by date):

A trinomial authority in parentheses indicates that the subspecies was originally described in a genus other than Thamnophis.

Anatomy and description

Common garter snakes are thin snakes. Few grow over about 4 ft (1.2 m) long, and most stay smaller. Most have longitudinal stripes in many different colors. Common garter snakes come in a wide range of colors, including green, blue, yellow, gold, red, orange, brown, and black.

Venom

Garter snakes have a mild venom in their saliva, which may be toxic to the amphibians and other small animals that they prey upon. For humans, a bite is not dangerous, and many handlers can attest to garter snakes gently biting in protest when held or restrained; these bites do not often break the skin, given the garter snake's smaller size, but may cause slight itching, burning, and/or swelling at the location of the bite. However, it is more likely that, prior to expending their energy through biting, garter snakes will secrete a foul-smelling fluid ("musk", "musking", "skunking") from postanal glands.

Common garter snakes are resistant to naturally occurring poisons in their prey, such as that of the American toad and rough-skinned newt, the latter of which can kill a human if ingested. Garter snakes (in addition to their own mildly venomous saliva) have the ability to retain poisons from their consumed amphibian prey, thus making them poisonous and deterring any would-be predators.

The common garter snake uses toxicity for both offense and defense. On the offensive side, the snake's venom can be toxic to some of its smaller prey, such as mice and other rodents. On the defensive side, the snake uses its resistance to toxicity to provide an important antipredator capability. A study on the evolutionary development of resistance of tetrodotoxin compared two populations of Thamnophis and then tested inside a population of T. sirtalis. Those that were exposed to and lived in the same environment as the newts (Taricha granulosa) or rough-skinned newt, that produce tetrodotoxin when eaten were more immune to the toxin (see figure).It seems that the two species were in an evolutionary arms race.