How Snakes Mate & Make Eggs

While the males of some species travel great distances to seek out females, others live at such high densities that the males needn’t travel far to find females. Some species with short active seasons breed in communal hibernacula before moving into the summer feeding habitats.

The males of some species engage in physical altercations over females. In these encounters, males intertwine their bodies, trying to push each other around. Sometimes, combat can escalate to biting. In other species, males do not fight with each other and may form “breeding balls,” in which several males vie to fertilize a single receptive female.

In most cases, courtship between males and females is brief. Males generally track and find females through the use of their forked tongues and vomeronasal systems. Once females are located, males seek out and find the females’ cloacas, and then attempt to align their bodies.

Inside their vents, snakes have chambers called cloacas, the openings to their reproductive and excretory systems. Males have paired intromittent organs, called hemipenes, one of which they use during mating sessions. When not in use, the hemipenes are inverted and held in the bases of their tails.

Once males have achieved cloacal juxtaposition, they will insert one of their hemipenes into the females’ cloacas. In some species and individuals, mating requires hours or more, which has led the males of many species to evolve spines, hooks and other protrusions on the end of their hemipenes that help to keep them in place. During the process, sperm swim over on the surface of the hemipenes and into the females’ vents.

Once the sperm have entered the females’ cloacas, they swim up the reproductive system to the oviducts. Some species engage in long-term sperm storage, while others store it for only a few days. Sperm wait in the oviducts for the arrival of the unfertilized eggs.

Eggs develop in the female snakes’ paired ovaries. Once mature, the eggs find their way to the oviducts, where the sperm are waiting. Over the next several weeks, the eggs are shelled -- those of egg-laying species are shelled thickly with calcium, while those of live-bearing species have transparent, soft membranes.

About two to four months after ovulation, the eggs are ready for deposition. Egg deposition sites vary between species, though they are invariably secluded locations. In live-bearing species, the mothers retain the young in their bodies for much longer. The young -- enclosed in uncalcified eggs -- hatch shortly before or during parturition.

Incubation time varies widely between species and individuals but normally takes approximately two to three months. Most females abandon their eggs immediately after parturition, but some -- notably pythons -- wrap themselves around the eggs until they hatch.

While most snakes reproduce sexually, scientists are discovering female snakes that -- at least occasionally -- reproduce without a male. According to Warren Booth, lead author of the 2012 study "Facultative Parthenogenesis Discovered in Wild Vertebrates," published in "Biology Letters," between 2.5 percent and 5 percent of the litters they studied were produced without fathers. The researchers suspect that this occurs when the mothers' sex cells have paired with each other to create embryos.