Garter snake is the common name for small to medium-sized snakes belonging to the genus Thamnophis in the family Colubridae. Native to North and Central America, species in the genus Thamnophis can be found in all of the lower 48 United States, and nearly all of the Canadian provinces south of the Northwest Territories and Nunavut—with the exception of Newfoundland and Labrador. They are found from the subarctic plains of west-central Canada east through Ontario and Quebec; from the Maritime Provinces and south to Florida, across the southern and central U.S. into the arid regions of the southwest and Mexico, Guatemala and south to the neotropics and Costa Rica.

Quick Facts Scientific classification, Species ...

Garter snake
The eastern garter snake (Thamnophis sirtalis sirtalis)
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Order:	Squamata
Suborder:	Serpentes
Family:	Colubridae
Subfamily:	Natricinae
Genus:	Thamnophis Fitzinger, 1843
Species
35, see text
Thamnophis distribution
Synonyms[1]
Atomarchus, Chilopoma, Eutaenia, Eutainia, Phamnovis, Prymnomiodon, Stypocemus, Tropidonote, Tropidonotus

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With about 35 recognized species and subspecies, garter snakes are highly variable in appearance; generally, they have large round eyes with rounded pupils, a slender build, keeled scales (appearing ‘raised’), and a pattern of longitudinal stripes that may or may not include spots (although some have no stripes at all). Certain subspecies have stripes of blue, yellow, or red, mixed with black tops and beige-tan underbelly markings. They also vary significantly in total length, from 18 to 51 in (46 to 130 cm).

With no real consensus on the classification of the species of Thamnophis, disagreements between taxonomists and disputed sources (such as field guides) are common. One area of debate, for example, is whether or not two specific types of snake are separate species, or subspecies of the same. Garter snakes are closely related to the genus Nerodia (water snakes), with some species having been moved back and forth between genera.

The first garter snake to be scientifically described was the eastern garter snake (now Thamnophis sirtalis sirtalis), by zoologist and taxonomist Carl Linnaeus in 1758. The genus Thamnophis was described by Leopold Fitzinger in 1843 as the genus for the garter snakes and ribbon snakes.^[2] Many snakes previously identified as their own genera or species have been reclassified as species or subspecies in Thamnophis. There are currently 35 species in the genus, with several subspecies in some of them.^[3]

Garter snakes are present throughout most of North America. Their wide distribution is due to their varied diets and adaptability to different habitats, with varying proximity to water. However, in the western part of North America these snakes are more aquatic than in the eastern portion. Garter snakes live in a variety of habitats, including forests, woodlands, fields, grasslands and lawns, but never far from water, often an adjacent wetland, stream or pond. This reflects the fact that amphibians are a large part of their diet. Garter snakes are often found near small ponds with tall weeds.

Garter snakes have complex pheromonal communication systems. They can find other snakes by following their pheromone-scented trails. Male and female skin pheromones are so different as to be immediately distinguishable. However, male garter snakes sometimes produce both male and female pheromones. During the mating season, this ability fools other males into attempting to mate with them. This causes the transfer of heat to them in kleptothermy, which is an advantage immediately after hibernation, allowing them to become more active.^[4] Male snakes giving off both male and female pheromones have been shown to garner more copulations than normal males in the mating balls that form at the den when females enter the mating melee. A snake hatch can include as many as 57 young.^[5]

Garter snakes use the vomeronasal organ to communicate via pheromones through tongue flicking, which gathers chemical cues in the environment. Upon entering the lumen of the organ, the chemical molecules will come into contact with the sensory cells, which are attached to the neurosensory epithelium of the vomeronasal organ.^{[citation needed]}

If disturbed, a garter snake may coil and strike, but it typically hides its head and flails its tail. These snakes will also discharge a malodorous, musky-scented secretion from a gland near the cloaca. This secretion from North American garter snakes contains seven highly odoriferous volatile components: acetic, propanoic, 2-methylpropanoic, butanoic, and 3-methylbutanoic acids; and trimethylamine, and 2-piperidone.^[6] They often use these techniques to escape when ensnared by a predator. They will also slither into the water to escape a predator on land. Hawks, crows, egrets, herons, cranes, raccoons, otters and other snake species (such as coral snakes and kingsnakes) will eat garter snakes, with even shrews and frogs eating the juveniles.

Being heterothermic, like all reptiles, garter snakes bask in the sun to regulate their body temperature. During brumation (the reptile equivalent of hibernation), garter snakes typically occupy large communal sites called hibernacula. These snakes will migrate large distances to brumate.

Despite the decline in their population from collection as pets (especially in the more northerly regions, in which large groups are collected at hibernation),^[16] pollution of aquatic areas, and the introduction of American bullfrogs as potential predators, garter snakes are still some of the most commonly found reptiles in much of their ranges. The San Francisco garter snake (Thamnophis sirtalis tetrataenia), however, has been on the endangered list since 1969. Predation by crayfish has also been responsible for the decline of the narrow-headed garter snake (Thamnophis rufipunctatus).^[17] Many breeders have bred all species of garter snakes, making it a popular breed.

Arranged alphabetically by scientific name:

In the above list, a binomial authority or a trinomial authority in parentheses indicates that the species or subspecies was originally described in a genus other than Thamnophis.

• Narcisse Snake Dens
• List of snakes, overview of all snake families and genera