Scientific name: Thamnophis sirtalis
Common name: Common Garter Snake
(Information in this Species Page was compiled by Michael Hosack in Biology 220W, Spring 2000, at Penn State New Kensington)
The Common Garter Snake is the most widely distributed snake in North America
and is very common on the nature trail. It is found from the Atlantic to the Pacific Oceans, into southern Canada (up to 68 degrees latitude) and into the desert southwest. It is most abundantly found in the eastern United States where it inhabits meadows, marshes, damp woodlands, gardens, fields, grasslands etc. Its principal habitat requirement is a nearby water source and is therefore most likely to be observed in the woods near the stream on our nature trail. There are many sub-species and varieties of garter snakes over this broad and diverse habitat range.
Adult individuals range in size from 40 to 90 cm with females being typically 50% larger than males. The Common Garter Snake has a great variety of color patterns and shades but characteristically
a light colored belly (yellow to pale green) and a prominent side stripe of tan, yellow or orange are indicative of the species. There may also be a variety of spots and reddish blotches that further add to the color diversity of individual specimens. There is also a recessive genetic trait that, in the homozygous state, generates an all black ("melanistic") form. These melanistic specimens may be abundant in certain habitats or in colder, more northern climate zones. The stripes of the garter snake not only contribute to its ability to effectively conceal itself in its habitat but also help to confuse potential enemies and predators as to its rate and direction of its movements. Garter snakes will attempt to flee if disturbed but can also secrete foul smelling anal secretions and will aggressively bite if provoked.
The Common Garter Snake hibernates in communal dens in logs, tree stumps, rock piles, and even in culverts and spaces under roads, railroad tracks and buildings. Dozens to hundreds of individual snakes can be found in these dens. In Canada one hibernation den had 8000 individual snakes! The Common Garter Snake is the first snake that emerges in the Spring (in early March depending upon local climate) and is the last snake to retreat into its hibernaculae in the Fall.
The Common Garter Snake mates immediately after emerging from hibernation. Eggs are retained in the female's uterus and develop through the spring and summer. The egg bearing female is particularly careful to use its environment and precise behavior patterns to maintain an optimum body temperature through the summer to ensure the efficient incubation of her eggs. The birth of the live young occurs in the Fall prior to hibernation. Typically 25 to 40 young comprise a "hatch", although up to 85 individuals have been reported. The mortality rate of these young is quite high. It takes three years for a Garter Snake to reach sexual maturity.
The Common Garter Snake is an opportunistic feeder and eats whatever prey items are available. Earthworms are a particularly important food source and garter snakes will feed heavily on them (up to 14 worms per hour!) when they are available. In addition to earthworms, garter snakes will eat frogs, tadpoles, fish, voles, salamanders, and even young birds. The garter snake is active during the day and swallows its prey alive. The swallowed prey either suffocates in the snake's stomach or is killed by the stomach's digestive secretions. The saliva of a garter snake has a mild venomous quality and is injected via its long, curved teeth in the back of its mouth. In some humans, swelling and rashes can result from the bite of a garter snake.
The garter snake finds its prey primarily by olfaction and via the chemical sensory system called
the Jacobson's organ (which involves the snake's tongue sweeping the air for scent molecules and then inserting the scent enriched tongue tips into two tiny pits in the roof of the mouth). Once a prey species is located, the actual attack and bite is mediated through both olfaction and vision.