Common Garter Snake

Common Garter Snake

NPS

Characteristics
Common Garter Snakes(Thamnophis sirtalis) have a range of color, but there is a basic pattern to their appearance. They generally have three light stripes that run the length of their body which has a black, brown, gray or olive background color. The dorsal stripe runs down the center of the snake’s back and two lateral stripes run down the body to the sides of the dorsal stripe.

The most typical color is yellow, with the dorsal stripe sometimes being darker yellow than the lateral stripes, but the stripes can also be white, blue, greenish or brown. Some snakes have checkered patterns of light rather than lines. Red blotches or a double row of black spots is often present between the stripes.

The belly color usually resembles the stripes. The head is wider than the neck and is basically dark colored. The tongue is red but tipped in black till just past where the forks come together. The eyes are round. The scales are keeled. They usually range from 3 to 4 ½ feet in length with the males being smaller. They can live to an age of ten years but average less than half that in the wild.

Prey and Predator
They generally prey on earthworms, amphibians, leeches, slugs, snails, insects, crayfish, small fish and other snakes. They seem immune to the toxic skin secretions of toads. Less frequently they will take small mammals, lizards and young birds. They hunt using their great sense of smell and their good vision. Their saliva is slightly toxic and may help them control their prey while they ingest them whole. They themselves fall prey to a variety of predators such as large fish, bullfrogs, snapping turtles, milk snakes, crows, hawks, great blue herons, raccoons, foxes, skunks, squirrels, shrews and domestic cats.

One of their most interesting predator prey relationships is with the extremely toxic Rough-skinned Newt. As the Garter Snakes adapted to be able to handle the toxins, the newt gradually increased their levels of toxin. Through time the levels of toxin in the Newts grew as the resistance of the snakes to the toxins changed. The Newts that did not increase their levels of toxin became prey and did not pass on their genes. The snakes that died from the toxins did not have many young.

The Most Common Snake
Common Garter Snakes are found throughout much of North America except the more arid areas of the southwest. They are the most common snake throughout much of their range. They prefer moist grassy environments and are often found near water such as ponds, lakes and streams and rivers. Sunny sections of meadows, oak patches, forest openings, and shrubby areas also provide suitable habitat.

They are found in urban and suburban areas where there is good cover to hide in. They will also flee into water when threatened. They are diurnal though on hot days they will seek out cooler places. They hibernate through the winter months in most of their range. The hibernacula may hold large numbers of garter snakes as well as other species.

Mating - Twists And Turns
The mating of Common Garter Snakes has some interesting twists and turns. The males emerge from the dens first and wait for the females to emerge. This cuts way down on the time needed to search for the females. Their complex system of chemical communication involves skin lipids that serve as pheromonal cues as the skin lipids of males and females are quite different. Some males are occasionally born with both female and male skin pheromones and those males will lead the unsuspecting males away from the dens, then hurry back to mate with as many of the emerging females as possible.

More often the emerging female will just check out the pheromones and choose a mate and then head for her summer range and a suitable place to give birth. The males stay by the den to mate with other emerging females. The females however have the ability to store the male’s sperm until it is needed, so she may not mate if she does not find a suitable partner. However sometimes the many suitable males will form a “mating ball” of several males around just one female, and thus several different males may fertilize eggs within the same brood.

Youthful Enthusiasm
The mating thus may take place in March or April and the 5-9 inch young are born in July or August after a gestation period of two to three months. Most litters range from 10-20 young although some have ranged up to 85. The larger females produce the larger litters. The new born snakes tend to stay around the mother for several hours or days, but she provides no parental care or protection.

The young eventually figure it out. They are on their own. The males reach sexual maturity in about a year and a half and the females follow suit in two to three years. Maybe this complex system, with its many opportunities for mating, is why the Common Garter Snake is so abundant.