The Web of Life (98-6) Snake Reproduction


Snakes often appear indifferent to their kind, but mating season brings a different temperament. Almost all snakes have courtship behaviors that precede mating.

A male searches out a receptive female by following her scent trail, left by secretions from glands in her tail as she moves. All snakes leave a scent trail from a pair of these anal glands.

On approach, a male works his way forward over her body with quick, quivering massage movements, while rubbing his chin along her back. Boas and pythons use their vestige hindlimb claws to caress. The male is constantly flicking his tongue in and out, savoring her scent.

When he reaches the nape of her neck, he maneuvers into mating position by looping his body over the lower part of her back and entwining his tail about the opening of her cloaca. The cloaca is the shared portal for the tail end of the digestive tract and the reproductive tract.

If the female is willing, she responds by raising her tail slightly and opening her cloaca. The male everts one of his hemipenes and copulates with her.

A hemipenis is a male snake’s penis, which is usually tucked inside the body. Males have a pair of hemipenes. They often alternate between the two for successive copulations.

Mating may be a prolonged affair, lasting hours. In species where a female is likely to mate with multiple males, a male often extends his copulation time. After sperm transfer, he may insert a plug that reduces the likelihood that other males can inseminate her.

In some snake species, females may be surrounded by several suitors. The rivals passionately try to mate with her while squeezing out the competition. The result is often a mass of entwined snakes; a behavior termed balling.

Aquatic snakes are prone to balling. A breeding ball of anacondas may contain 10 or more males, all coiled around a single female. They may stay knotted together for up to 4 weeks.

Aside from balling, nuptial combat among males is common in rattlesnakes, vipers, mambas, pythons, and some colubrids. (Colubrids comprise the most specious snake family, with over 2/3rds of all kinds of snakes.) These are typically bloodless rituals: determinations of strength and stamina. One eventually concedes and slithers away. Male adders get so wrapped up in their ritualistic combat dance that they may continue even after the rival has been replaced with a stick.

Fertilization does not necessarily occur immediately after copulation. A female has control over her fertilization.

Sperm can survive in the female reproductive tract for a considerable duration. Females of some species in captivity, having been kept away from males for several years, may birth healthy offspring. (Some snakes lay eggs (oviparity), while others give birth to live young (viviparity).)

Snake parental care is generally quite limited. A female may guard a clutch of eggs for a few days. Some adaptations are more elaborate. The Indian python uses its body heat to warm eggs through muscular contractions.

The king cobra uniquely builds a complex nest, with eggs deposited in the center, in a cavity covered with earth, leaves, and grass. A mother king cobra remains nearby, defending the eggs from intruders.

Rattlesnakes stay with their newborn young for a week or more; a rare instance in neonatal maternal care in snakes.