Are snakes viviparous or oviparous? A detailed explanation of snake reproductive methods

Snakes are true terrestrial vertebrates. There are currently more than 3000 species of snakes worldwide. They feed mainly on rodents (and also on frogs, birds, etc.). They prefer shaded, humid, rarely visited environments with dense weeds, luxuriant trees, hollow stumps or piles of rocks, woodpiles and grass heaps, old ridge earth walls, and abundant food. Let us take a look below at whether snakes are viviparous or oviparous!

Are snakes viviparous or oviparous?

Some snakes are oviparous, and some are ovoviviparous. Snakes in the family Colubridae are all oviparous. Some snakes in the families Pythonidae, Typhlopidae, and Elapidae are oviparous, while others are ovoviviparous. Snakes that usually live in cold regions and high mountains are mostly ovoviviparous, such as the boa constrictor. This mode of reproduction allows the eggs to remain in the mother's oviduct, so that the developing embryos can maintain the temperature they need and are not affected by the variable external environment. Almost all sea snakes are also ovoviviparous.

What does ovoviviparous mean?

Ovoviviparous means "internal incubation of eggs". That is, the fertilized eggs produced by internal fertilization remain in the mother's reproductive tract, and develop into young using the yolk of the egg itself, and are only born after the embryos are fully developed. Once mature, the mother's reproductive tract contracts to expel the young together with the egg membrane. Therefore, the embryos of ovoviviparous animals receive proper protection from the mother, and the survival rate of hatching is more assured than that of oviparous animals. When the fertilized egg develops, in addition to using the nutrients of the yolk, the exchange of gases and the maintenance of moisture required for its development still depend on the mother's supply.

What are the oviparous snakes?

1. Five-paced snake (Deinagkistrodon acutus): The eggs of the five-paced snake are mostly laid in natural caves with shallow, short, and dry passages. The number of eggs laid varies. Young female snakes lay eggs early but in small numbers, while old female snakes lay eggs late but in large numbers, generally 12-18 eggs. The eggs are white, oblong, with soft shells that feel like paper to the touch. When laid, the eggs are mostly arranged upright in circles, sticking together, and are usually all laid within 1-3 days. The young snakes hatch in about 24 days, and are 19 cm long at hatching.

2. Many-banded krait (Bungarus multicinctus): The many-banded krait is oviparous. The snakes often begin hibernation in mid-November and emerge from hibernation in early May of the following year. They mostly lay eggs in June, 3-12 eggs each time. The incubation period requires 45-56 days, and the young snakes reach sexual maturity after three years. They inhabit plains, hills, or near water at the foot of mountains, and are active in the evening or at night. They are often found at field edges, roadsides, graveyards, and vegetable gardens.

3. Big-eyed rat snake (Zaocys dhumnades): The big-eyed rat snake is oviparous. The female snakes lay eggs from July to August, 7-30 eggs each time, and the incubation period is 45-50 days. Female snakes account for 51% of the male-to-female ratio, fertilized eggs account for 91.4% of the eggs laid, the natural hatching rate is 64.6%, and the natural survival rate is 30%. They mostly inhabit plains, low mountain areas, or hills, and can often be seen in fields and farmhouses. From late spring to early autumn, they often appear near farmland and farmhouses.

What are the ovoviviparous snakes?

1. Pit viper (Gloydius): The pit viper is ovoviviparous. The embryos develop inside the female snake's body, and the young snakes can live independently after birth. Because this reproductive method can give the young snakes the best protection, the survival rate is very high. From May to September each year is the breeding period of the pit viper, and each female pit viper can give birth to 2-8 young snakes. The newly born young snakes are 14-19 cm in body length and weigh 21-32 grams.

2. Sea snake: Fully aquatic sea snakes are ovoviviparous, giving birth to 3-4 young sea snakes 20-30 cm long each time. Sea snakes that can come ashore remain oviparous. During the egg-laying season, they often go in groups to fixed islands to lay eggs. Gato Island in the Philippines is one of the islands that sea snakes often visit. For many years, people have carried out commercial snake-catching activities on these islands.

3. Boa constrictor: The boa constrictor has larger rostral scales at the front, which are horizontally angular, but the scales toward the rear gradually become smaller. The body is barrel-shaped, and the tail is relatively short with a rounded tip, making the appearance resemble a head that has been injured. The whole body is brown. It inhabits deserts and dry areas. It is ovoviviparous, mating in water or at the water's edge. After 9 months, the female gives birth to 18-42 young snakes, each more than 62 cm long.