With a blanket of snow on the ground we don’t expect to see local reptiles or amphibians but, as the days get longer, we are more likely to encounter our cold-blooded neighbors. In February, you can find spotted salamanders walking slowly under the ice, looking for mates. Later in the month, the noise of woodfrogs, spring peepers, and chorus frogs advertise territories. Amidst this flurry of amphibian breeding, garter snakes begin to emerge from their hibernacula. Though garter snakes relish a frog or salamander meal during the summer, this time of year they have one goal—mating.
Our resident garter snake
Can you find the garter snake?
Keeping an eye on visitors
Male garter snakes emerge first, when the air temperature is still in the 30’s, to prepare for mating. On sunny days you might find one basking on a snowbank. Around March or April, the much larger, stout-bodied females will begin to emerge and will soon be surrounded by skinny males vying for a chance to fertilize the eggs she is carrying internally. Though “breeding balls” of dozens to hundreds of males are famous, in Chicagoland I usually only find 2-6 males per female. Interestingly, some males will behave like females. Apparently this behavior attracts other males who, when they pile on in an attempt to mate, help warm the imposter. At the same time, the ill-fated suitors are more likely to be eaten by predators, providing both a shield and decreasing the number of competitors for actual females.
Once bred, female garter snakes retain their eggs (known as ovoviviparity) rather than lay them in a rotting log, like a rat snake. In this way it is easy for the female to move the eggs from one warm patch of sun to another, even in places where the ground stays very cold late into the summer. This behavior has allowed garter snakes to spread further north than any other group of snakes and ensures that garter snake babies are born earlier in the year than any other snake. It also explains the biology behind all the stories of kids bringing one big garter snake home, only to later find the house full of pencil-sized baby snakes.
Chicago is home to a particularly striking form of the Garter Snake. It is found only in southeastern Wisconsin, northeastern Illinois and extreme northwestern Indiana in the vicinity of Chicago. The Chicago Garter Snake has a dark grey head and prominent broad black bars on its sides that break up the lateral stripes. If you can't go out looking for Garter Snakes yourself, you'll find the Nature Museum's resident Chicago Garter Snake in our Istock Look-In Lab.