According to Marshall University, there is an average of 10 to 20 babies in a litter of garter snakes. However, the size of litters runs from seven to 100, varying by the size of the mother snakes. Larger snakes have larger litters.
The University of Michigan points out that garter snakes typically mate in spring when hibernation has concluded. Males sometimes mate with more than one female. Garter snakes do not lay eggs. The babies develop inside their mother for two to three months, and then they are born alive, usually between July and October. As soon as they are born, baby garter snakes are on their own.