Garter snake

Taxonomy and Description

The genus Thamnophis was formally described by zoologist Leopold Fitzinger in 1843, though the first species, the eastern garter snake (Thamnophis sirtalis sirtalis), was scientifically described by Carl Linnaeus in 1758. Taxonomic classification within the genus remains an area of active debate among herpetologists, with disagreements over species versus subspecies status and frequent historical reclassifications, as many snakes previously identified as their own genera have been reclassified into Thamnophis. The Reptile Database currently recognizes 37 distinct species within the genus, many of which are further divided into numerous subspecies, and garter snakes are closely related to water snakes of the genus Nerodia, with some species having been moved back and forth between these genera over time due to shifting taxonomic perspectives. With about 37 recognized species and 52 subspecies, garter snakes are highly variable in appearance. Generally, they have large round eyes with rounded pupils, a slender build, and keeled scales which appear raised. They have 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 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. This complexity extends to debates over whether certain types are separate species or merely subspecies of the same species, highlighting the ongoing scientific work to understand the relationships within the genus Thamnophis, and it is an area of debate, for example, whether two specific types of snake are separate species, or subspecies of the same.

Distribution and Habitat in Canada

Native to North and Central America, species in the genus Thamnophis can be found in all of the lower 48 United States, and all of the Canadian provinces. They are found from the subarctic plains of west-central Canada east through Ontario and Quebec, and from Atlantic Canada south to Florida. Their range extends 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. Their wide distribution is due to their varied diets and adaptability to different habitats, with varying proximity to water.

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 prefer habitats that offer mixed canopy cover, allowing for proper thermoregulation and reducing the risk of overheating. Their wide distribution is due to their adaptability to different habitats with varying proximity to water.

Garter snakes are not originally native to the eastern Canadian island of Newfoundland, but have been breeding there in the wild and gradually spreading since at least 2010. It is unknown how they reached the island, probably accidentally via hay shipments or as escaped pets. In the western part of North America these snakes are more aquatic than in the eastern portion. However, they are never found far from water in any region, as water is a constant requirement in their ecology.

Behaviour and Ecology

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. In spring, these dens become the focal point for mating activities, with mating balls forming as multiple males attempt to court a single female.

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. 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.

During the mating season, this ability of some males to produce female pheromones 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. 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.

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. 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.

Social Group Dynamics

A long-term study by the Ontario Ministry of Transportation has shed light on the social behavior of Butler's garter snakes. The study, conducted in a 250-hectare area near Windsor, Canada, tracked over 3,000 individual snakes over a 12-year period. The findings challenge previous assumptions about solitary snake behavior and suggest that these snakes form social groups and communities. The study revealed that Butler's garter snakes do not wander randomly but instead tend to associate with specific groups of snakes. These groups typically consist of three to four individuals, with some larger groups reaching up to 46 snakes.

Diet and Unique Toxicity

Garter snakes, like all snakes, are carnivorous, and their diet consists of almost any creature they are capable of overpowering, which makes them highly adaptable feeders. They consume prey including slugs, earthworms such as nightcrawlers, as redworms are toxic to them, leeches, lizards, amphibians including frog eggs, minnows, and rodents, and when living near water, they eat other aquatic animals as well. The ribbon snake (Thamnophis saurita) in particular favors frogs including tadpoles, readily eating them despite their strong chemical defenses, and food is swallowed whole by all garter snakes during feeding. Garter snakes often adapt to eating whatever they can find and whenever they can find it because food can be either scarce or abundant in their environment, and although they feed mostly on live animals, they will sometimes eat eggs if the opportunity presents itself.

Garter snakes were long thought to be non-venomous, but discoveries in the early 2000s revealed that they produce a neurotoxic venom. Despite this, garter snakes cannot seriously injure or kill humans with the small amounts of comparatively mild venom they produce and they also lack an effective means of delivering it. In a few cases, some swelling and bruising has been reported. They do have enlarged teeth in the back of their mouths but their gums are significantly larger and the secretions of their Duvernoy's gland are only mildly toxic.

As garter snakes may retain toxins from their amphibian prey in their liver, they are one of the few species of snakes in the world that can be both venomous and poisonous. Garter snakes feeding on toxic newts can also retain those toxins in their liver for weeks, making those snakes poisonous as well as venomous. Evidence suggests that garter snake and newt populations share an evolutionary link in their tetrodotoxin resistance levels, implying co-evolution between predator and prey. This represents a case of co-evolution where predator and prey have shaped each other over time.

Conservation Status and Threats

Overall, garter snakes remain common and widespread reptiles throughout much of their range, including Canada, and they are still some of the most commonly found reptiles in much of their ranges due to their adaptability. However, specific populations face significant threats from human activity and environmental change, and the San Francisco garter snake (Thamnophis sirtalis tetrataenia) has been on the endangered list in the United States since 1969 due to habitat loss and fragmentation. The narrow-headed garter snake (Thamnophis rufipunctatus) has also declined, and predation by crayfish has been responsible for this decline, showing how introduced species can impact native wildlife. Threats to garter snakes include pollution of aquatic areas and the introduction of American bullfrogs as potential predators. In the more northerly regions, in which large groups are collected at hibernation, collection as pets has contributed to population declines. Despite these pressures, their varied diets and adaptability to different habitats have allowed most species to maintain stable populations. Many breeders have bred all species of garter snakes, making it a popular breed.

Reproduction and Life Cycle

In early spring, snakes emerge from their communal hibernacula for mating. Mating occurs at the den site, leading to the formation of large mating balls where multiple males compete for a single female. This intense competition is mediated by complex pheromonal communication systems. Most garter snake species are ovoviviparous, meaning they give birth to live young rather than laying eggs, which is an adaptation to cooler climates.

The developing embryos are retained within the mother's body until they are fully developed. Litter sizes can be substantial, reflecting the need for high reproductive output in an environment with many predators. A single hatch can include as many as 57 young. The newborn snakes are independent from birth, equipped with venom and fully functional sensory systems.

The newborn snakes must immediately begin foraging for small prey like earthworms while avoiding predators that target juveniles, including shrews and frogs. Their growth rate is influenced by food availability in their first year. They will reach sexual maturity in two to three years, at which point they will migrate back to traditional hibernation sites to brumate and eventually mate. They use the vomeronasal organ to communicate via pheromones through tongue flicking from a young age.

Selected Species and Subspecies

• Common Garter Snake (Thamnophis sirtalis): The most wide-ranging species in North America, with numerous subspecies including the Eastern (T. s. sirtalis) and the endangered San Francisco garter snake (T. s. tetrataenia), and it is highly variable in colour and pattern across its vast range.
• Butler's Garter Snake (Thamnophis butleri): A species with a limited range in the Great Lakes region, notable as the subject of the extensive Ontario social behaviour study, and it is a small, secretive snake often found in moist grasslands.
• Plains Garter Snake (Thamnophis radix): Inhabits grasslands and prairies across central North America, including the Canadian Prairies, and it is characterized by a bright yellow or orange stripe down its back and a distinctive checkered pattern.
• Ribbon Snake (Thamnophis saurita): A particularly slender and aquatic species, often found in eastern North America near water bodies, and it has a very long tail and a strong preference for amphibian prey like frogs.
• Western Terrestrial Garter Snake (Thamnophis elegans): A highly variable species found in western North America, from British Columbia southwards, and its diet can include a higher proportion of rodents compared to other garter snakes in the genus.
• Narrow-headed Garter Snake (Thamnophis rufipunctatus): A threatened species in the southwestern United States, facing significant pressure from non-native crayfish predation and habitat alteration near streams.
• Checkered Garter Snake (Thamnophis marcianus): Found in the southwestern U.S. and Mexico, recognized by the distinct checkered pattern between its stripes, and it is often associated with arid and semi-arid environments.
• Short-headed Garter Snake (Thamnophis brachystoma): A smaller species with a restricted range in Pennsylvania and New York, often associated with open fields and meadows, and it has a notably shorter head compared to its body.

Questions about Garter snake

Are garter snakes in Canada venomous?

Yes, garter snakes produce a mild neurotoxic venom, a discovery made in the early 2000s. However, they cannot seriously injure or kill humans with the small amounts of comparatively mild venom they produce. They lack an effective means of delivering it, having enlarged teeth in the back of their mouths but significantly larger gums. In a few cases, some swelling and bruising has been reported from bites.

What do garter snakes eat?

Garter snakes are carnivorous. Their diet consists of almost any creature they are capable of overpowering: slugs, earthworms, leeches, lizards, amphibians, minnows, and rodents. The ribbon snake in particular favors frogs, including tadpoles. Food is swallowed whole. They often adapt to eating whatever they can find because food can be either scarce or abundant. Although they feed mostly on live animals they will sometimes eat eggs.

What is the difference between a garter snake and a ribbon snake?

Ribbon snakes are a group within the garter snake genus Thamnophis, with the scientific name Thamnophis saurita. They are generally more slender and have a proportionally longer tail. Behaviourally, they are often more strongly associated with aquatic habitats and have a noted preference for amphibians, especially frogs and tadpoles. They are considered a distinct lineage within the broader garter snake classification.

Where do garter snakes go in the winter?

Garter snakes occupy large communal sites called hibernacula during brumation, which is the reptile equivalent of hibernation. They will migrate large distances to reach these brumation sites. Being heterothermic, like all reptiles, they rely on external heat sources to regulate their body temperature, which is not possible during the cold winter months. These hibernacula are often used year after year by the same communities of snakes. In the spring, they emerge from these communal dens to bask in the sun and participate in mating activities, often at the den site itself, before dispersing for the summer season.

How did garter snakes get to Newfoundland?

Garter snakes are not originally native to the eastern Canadian island of Newfoundland. However, they have been breeding there in the wild and gradually spreading since at least 2010. The exact method of their arrival on the island remains unknown. It is probable that they reached Newfoundland accidentally, potentially through human activities such as being transported in hay shipments. Another plausible explanation is that they arrived as escaped or released pets. Their presence and establishment on the island represent a recent expansion beyond their historical native range in North and Central America.

Are garter snakes social animals?

A long term study on Butler's garter snakes has shed new light on their social behaviour, challenging previous assumptions that they are purely solitary. The study, conducted over 12 years and tracking over 3000 individual snakes, revealed that these snakes do not wander randomly. Instead, they tend to associate with specific groups of snakes, forming distinct social groups and communities. These groups typically consist of three to four individuals, though some larger groups can reach up to 46 snakes. This research suggests a more complex social structure than was traditionally attributed to garter snakes and many other snake species.

Sources and further reading

• Garter snake (Wikipedia)
• Maritime Garter Snake (museum.novascotia.ca)
• Garter Snake Care Sheet (petmd.com)
• How to take care of your Garter snake (rspca.org.uk)
• Garter Snake Fast Facts (nps.gov)

Checked by the Your Space Hamilton desk. Last updated 2026-10-21.