A Garden of Common Garter Snakes
Also known as the eastern garter snake, the common garter snake (Thamnophis sirtalis) is a species of snake found throughout North America. Populations can be found in almost any habitat and many are highly adapted; currently there are 13 recognised subspecies with distinct morphologies and behaviours. Most commonly garter snakes are found in forests, grasslands, wetlands, and rural and agricultural areas and are a popular sight for beginner herpetologists.
The appearance of the garter snake can vary greatly depending on area and subspecies. In general, T. sirtalis can be identified by a dark, usually black, brown, or olive body with three yellow, white, green, or blue stripes running down the back and sides, and a light underside. Some garter snakes will also sport red or dark brown spots, sometimes creating the appearance of being totally red. The best way to identify common garter snakes is by the scales around their mouths, which sport distinctive black stripes. Most individuals grow to be 40-60cm long and weigh about 150g, although some have been recorded at over 1m.
Although most consider the common garter snake to be non-venomous, they actually do produce a mild venom. This is most useful when hunting, as T. sirtalis feeds on a variety amphibians and small mammals. In addition to their venom, some populations have also developed a resistance to a toxic chemical called tetrodotoxin which is produced by a common prey animal the rough-skinned newt (Taricha granulosa). This adaptation has pitted the two species against each other in an evolutionary arms race, where the rough-skinned newt grows more toxic and the common garter snake becomes ever more resistant. In addition to these hunting measures, T. sirtalis will spray a foul-smelling fluid when threatened by predators such as hawks, snapping turtles, bullfrogs, large fish, and predatory mammals.
Like most snakes, T. sirtalis is active during the day. As ectotherms they rely on the weather to regulate their internal temperatures, so they are most often seen in the warmer spring and summer months. In their southern range the common garter snake is active year-round, and in colder areas they hibernate from October to March. Males emerge from hibernation first and form large ‘mating balls’ around emerging females, consisting of up to 20 individuals wrapping around each other in an attempt to reach the female. This allows the female to warm up faster and be ready to mate. Some tricky males will emit the same pheromones as females when emerging in order to recieve the same treatment; in this way they too are able to warm up more quickly and can reach ready females faster than their competitors. Females are oviviparous, meaning they develop eggs inside the body. After a gestation period of 2-3 months, up to 40 young are born live. They become sexually mature at about 2 years old and can live up to 6 years in the wild.
Conservation status: Because of their wide range and large population, the common garter snake is rated Least Concern by the IUCN. One subspecies, the San Fransisco garter snake (Thamnophis sirtalis tetrataenia), is considered endangered due to habitat loss and water pollution, which seriously impacts the availability of prey.
Mark Kluge (via iNaturalist)
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