The natural history of snakes is endlessly fascinating and variable! We’ll keep our focus fairly narrow here, discussing the natural history of snakes in the upper Midwest, particularly Wisconsin.
So how do snakes survive in our temperate region, where weather conditions (e.g. freezing temperatures) can be deadly to an animal like a snake? Let’s examine a year in the life of a Wisconsin snake.
During a large percentage of the year, Wisconsin snakes hibernate, i.e. become dormant. Snakes are ectothermic, depending on behavior and features of their environment, for regulating their body temperature. This means that during about half the year in Wisconsin, conditions are such that a snake aboveground would not survive. Instead, many snakes hibernate from about mid-October until mid-April each year. Some snakes, such as garter snakes, which are more cold-tolerant than other species, spend more of the year above ground and may be seen as late as November in the fall and as early as March in the spring. Wisconsin’s two species of rattlesnakes, on the other hand, will often enter hibernation in September and not emerge until mid-May. Hibernacula (overwintering areas) are varied, with many snakes using old crayfish or small mammal burrows and others using rock outcrops to work their way underground to avoid the frost line. Many snakes will hibernate partially submerged in water.
When snakes first emerge from hibernation in the spring, they are quite cool and slow-moving. Some, like garter snakes, will spend a considerable amount of time around their hibernaculum before they disperse on the landscape. In fact, garter snakes take care of breeding while still around the hibernaculum. It’s a real treat to come upon a “mating ball” of garter snakes, with a great number of males competing for the right to breed with one of the larger female snakes.
Snakes spend time basking in the sun to increase their body temperatures and their metabolisms in the spring. As soon as they are ready, they will then seek out food and in many cases, mates. Most of Wisconsin’s snakes breed in the spring, with the exception of our two rattlesnakes, which mate in the summer primarily. Males will seek out females for breeding in July and August, and the females store the sperm from these matings until the following spring, giving birth to the young in late August or September of that year. In Wisconsin, we have snakes that lay eggs (oviparous), snakes that retain their young in membranous egg sacs (ovoviparous) until birth, when the youngsters use an egg tooth at the tip of their snouts to free themselves from the egg sacs, and viviparous snakes, where the young are born live. Most of Wisconsin’s egg-laying snakes lay their eggs in June but the gray ratsnake may not do so until July. Our live-bearing snakes, the garter snakes, will give birth to their young sometime in August or September.
Snakes lead a fairly solitary life for most of the year, hunting for meals, which can vary from ants to bats or pocket gophers, in Wisconsin. Adult snakes may shed their skins late in the spring or early summer. Younger snakes, which are faster growing than adults, will often shed their skins more than once during their active seasons to accommodate their growth. Snakes also spend time avoiding predators and finding places where they can regulate their body temperatures to keep themselves comfortable and avoid getting too hot, which can be lethal, during their active seasons.
As the days start to shorten in late summer, snakes begin their journeys back to the areas where they will overwinter, although some may stay active until late in October, depending on the weather.