Smooth snakes hibernate from around October in groups of up to 30 snakes. They emerge from hibernation in March or April to feed and possibly to mate. Mating takes place in April and May, with females incubating the eggs inside their bodies, then giving birth to up to 15 live young that look like miniature adults in September or October. Females do not breed every year. The smooth snake has a relatively long life span of up to 20 years, so the need to breed regularly is less and they will often not breed in years where food is more scarce.