While many snake species lay eggs, a notable portion gives birth to live young, an adaptation that allows them to thrive in various environments.
How Snakes Reproduce
Snakes employ three primary reproductive strategies: oviparity, ovoviviparity, and viviparity. Oviparity, the most common method, involves the female laying eggs that develop and hatch outside her body. Approximately 70% of snake species, including pythons and corn snakes, reproduce this way, often depositing their clutches in burrows or nests. Most oviparous species abandon their eggs after laying them, though some, like certain pythons, coil around them to provide warmth and protection.
Ovoviviparity involves the retention of eggs within the mother’s body, where the young develop and hatch internally before being born alive. In these cases, there is no direct placental connection, and the developing embryos primarily rely on the yolk sac for nourishment. Rattlesnakes and many boa constrictors utilize this method, offering protection to the developing offspring without the risks associated with external eggs.
Viviparity, or true live birth, is less common but represents a more advanced form of internal development. Here, the young develop inside the mother with a direct placental connection, receiving nutrients directly from her bloodstream, similar to mammalian reproduction. Viviparous snakes do not involve eggs at any stage of development.
Viviparity: True Live Birth
In true viviparity, embryos develop entirely within the mother’s body, receiving continuous nourishment directly from her via a placenta-like structure. This structure, often derived from the yolk sac, facilitates the transfer of oxygen, water, and nutrients to the developing offspring. Unlike ovoviviparity, where embryos rely solely on the yolk reserves within an egg, viviparous young receive ongoing maternal support throughout their development. This direct nutritional exchange ensures the sustained growth of the young until they are fully formed and ready for birth. The mother’s body essentially acts as a protective and nourishing incubator, eliminating the need for external egg cases.
Snakes That Give Live Birth
All species within the Boidae family, including boa constrictors and anacondas, are viviparous. Boa constrictors typically produce litters of 10 to 65 young, while green anacondas, among the largest snakes, often have 20 to 40 babies, which can be nearly two feet long at birth. Several viper species are also viviparous, such as certain pit vipers. Sea snakes, with the exception of sea kraits, are almost entirely viviparous because they rarely or never visit land, and snake eggs cannot develop underwater. Water snakes, belonging to the Colubrid family, are another example of viviparous snakes, likely due to the challenges of finding dry nesting sites in their wet habitats.
The Advantages of Live Birth
Live birth in snakes offers several advantages, particularly in challenging environments. Retaining developing young inside the mother provides protection from external predators, which might otherwise consume vulnerable eggs left in nests. This internal incubation also shields the embryos from environmental hazards like harsh weather conditions or fluctuating water levels. Temperature regulation is another significant benefit, as the mother can actively move to warmer or cooler areas, such as basking in the sun or seeking shade, to optimize the development of her offspring. This ability is particularly advantageous in colder climates or high altitudes where external egg incubation might be difficult or impossible due to freezing temperatures. Live-born young are also often more developed and mobile at birth, increasing their immediate survival chances by being ready to fend for themselves sooner.