Since snakes generally avoid human contact and have secretive habits, people don't often observe mating. Snakes mate after leaving hibernation in spring. Females lay a scent trail for males to follow. Courtship behavior varies depending on the species. During mating, the male snake inserts a copulatory organ called the hemipenes into the cloaca of the female to transfer sperm. Male and female snakes are similar in appearance, and have to be examined to determine sex.
Once a male finds a female snake, there may be a form of courtship. Some kinds of male snakes have nuptial tubercles they rub over parts of the female's body; other species use their bodies in rubbing the female; and yet others ripple their muscles as they lie next to the female. Male snakes often rub their heads against the female, and they may entwine their bodies. After a brief courtship, snakes begin mating.
The male snake everts the hemipenes through his cloaca from their storage sac in the tail. Sperm go down an external groove in the organ. The sperm either fertilize the eggs directly or go to a storage receptacle. Some female snakes can store viable sperm for months to years, and don't need to mate each time they produce fertile eggs. Most snakes lay eggs, but some species keep the developing embryos in the oviduct and release living young.