There are two major categories of snakes: oviparous and viviparous. Viviparous snakes give birth to live young ones while oviparous lay eggs. 30% of snake species give live birth while 70% are oviparous.
There are about 3000 snake species in the world. While the snakes’ general anatomy and body systems are pretty general across the board, different species exhibit varying characteristics in different aspects, such as methods of reproduction.
What are Viviparous Snakes?
Viviparous snakes are snakes that give birth to live young ones. The embryo develops in the mother’s womb, where it is nourished via the mother’s placenta or yolk sac
Viviparity in snakes is quite unorthodox as most reptiles, including a large number of snake species, are known to lay eggs.
Usually, viviparity is a primary characteristic of mammals. Thus, it is safe to deduce that viviparity in snakes is linked to snakes with unusual anatomical and behavioral specializations.
Examples of Viviparous Snakes (List)
As members of the Boa family (family Boidae), anacondas are viviparous. There are four species of anacondas – the yellow anaconda, the green anaconda, the Bolivian anaconda, and the darkly-spotted anaconda- all of which give birth to live young ones.
Anacondas are viviparous for two main reasons: their environment and the behavior of their predecessors. Anacondas live in wet places, mostly on swamps, marshes, and streams that are not fast-moving. While they spend enough time on land, they are exceptional swimmers and spend a lot of time in the water. Laying eggs in such an environment could be counterproductive.
Anacondas have a gestation period of about six months, after which they give birth to 20 to 100 babies. Baby anacondas are about 2 feet at birth, and they are born able to swim and ready to hunt.
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2. Sea Snakes
Sea snakes are also known as coral reef snakes in the family Elapidae and subfamily hydrophiinae. hydrophiinae are the snakes that inhabit seawater for most of their entire lifetime.
These snakes rarely visit the dry land, and eggs cannot develop and incubate underwater. Only a few sea snakes lay eggs, such as the kraits. As aforementioned, this species leaves the ocean to mate and breed. That said, most sea snakes are viviparous, and they give birth to young ones in the water where they live.
Some viviparous sea snakes include:
The yellow-bellied sea snake: This venomous sea snake lives in the Indian and Pacific oceans. It is fully adapted to sea life. It mates feeds, and gives birth to live young ones in the sea.
Spiny-Headed Sea Snakes: Also known as horned sea snakes or Peron’s sea snakes, they are mostly found in the western tropical Pacific Ocean. They are a viviparous species that give birth to up to 10 live snakes at a time.
Olive Sea Snakes: They are the most common sea snakes along the coast of northern Australia and the nearby islands. Olive sea snakes do not leave the water at all. The young ones of these sea snakes are born alive and spend the entirety of their lives in the sea.
Turtleheaded Sea Snakes: Turtleheaded sea snakes live in the sea and like swimming in shallow coral reef waters. They are viviparous and give birth to between 2-5 young per litter.
Beaked Sea Snakes: These snakes give birth to the biggest number of young ones in a single litter at an average of 18 and about a maximum of 30 baby snakes. Their young are also relatively large when they are born.
Northern Mangrove Sea Snakes: This species of sea snake is venomous and is endemic to Australian and New Guinea waters. They are among aquatic snakes that give birth to live young ones in water bodies, making them viviparous.
3. Water Snakes
Water snakes are non-venomous members of the family Colubridae that are native to North America. They are among the few members of this family that are viviparous.
They spend most if not all of their time in freshwater bodies like swamps and slow-moving streams that make it difficult for them to lay eggs.
The difficulty in laying and nurturing eggs in wet habitats is the primary reason water snakes evolved to become viviparous. Furthermore, snake eggshells are thin, which makes it very possible for them to drown.
For these reasons, water snakes’ eggs develop internally and where the mother provides nutrients through the placenta or the yolk sac.
4. Boa Constrictors
Boa constrictors are significantly smaller than anacondas. Like the anacondas, they are viviparous and give birth to live young ones, with a gestation period of four to five months. They give birth to 10 to 65 young ones at a time.
Boa constrictors breed during the dry season, and the males mate with several females. Unlike some other species, it is not known why they give birth to young. The most likely reason is the kind of environment their ancestors lived in, forcing them to evolve. Baby boa constrictors are born at 2 feet in length.
5. Amazon Tree Boas
This tree boa is an arboreal species whose range lies in the Amazon and South Central American countries. Just as expected of the Boa family, they are viviparous and thus, give birth to live young ones.
These boas reach sexual maturity at the age of three. Their gestation period lasts 6 to 8 months, which is the longest among Boas. When the time is due, amazon tree boas give birth to between 8 and 14 babies per year, who exhibit independence from the word go.
Rattlesnakes are highly specialized, venomous reptiles and have a large, strong body, and are very aggressive.
Predators would not want to mess with a deadly gravid rattlesnake, so the eggs are very safe growing inside the mother’s womb.
Rattlesnakes gestate for about three months, after which they give birth to between 10 and 60 live baby rattlesnakes.
Related Article: Do Rattlesnakes Give Birth or Lay Eggs?
Also known as ringhals or ring-necked spitting cobras, rinkhals are deadly venomous elapid snake species.
They are common in Southern African countries. While they are related to cobras which are egg-laying, rinkhals are viviparous. So, they give birth to live young ones.
Their venomous nature means that their eggs are safe inside the womb as no predator would gain any form of access without the snake defending herself and her young ones. This is the most likely reason why they developed this reproductive method.
The annual mating season for rinkhals is between June and August, and they give birth in the period between December to February or early March.
8. White-Lipped Snakes
These are small-sized species of venomous snake in the family of elapids.
They are one of the most cold-adapted snakes native to Australia, surviving at high altitudes and southern latitudes where a few other snake species live.
Due to their native environment of cold areas, they evolved to become viviparous, where they keep their eggs in their body and give birth to live young ones.
How Snakes Became Viviparous
It is believed that viviparity developed early on in the history of snakes. According to theory, viviparous snakes emerged from oviparous snakes as a factor of natural selection.
When laid eggs were in danger due to environmental factors, a female would retain the eggs much longer in her womb, thereby progressively shortening the period between deposition and hatching. The reverse from viviparity to oviparity is highly unlikely.
Snakes that became viviparous over time are those whose females are not adequately self-defensive to protect eggs from predators, those who live in cold climates, and those whose eggs would face environmental risks. As such, most viviparous belong to three categories of snakes: boas, vipers, and aquatic snakes.
Viviparous snakes are those snakes that give birth to live young ones. According to theory, viviparous snakes evolved from oviparous snakes as a response to natural selection.
Most viviparous snakes are those that live in cold climates, live in aquatic environments, or are venomous. As such, most viviparous snakes are boas, vipers, and aquatic snakes.
Joe is a freelance writer for FaunaFacts. Joe has written extensively about snakes for the site, but also contributes content about a range of animals.