Are Pythons Viviparous or Ovoviviparous? Unveiling the Truth About These Large Arboreal and Aquatic Snakes

In common knowledge, snakes are all oviparous because they lay eggs, but in fact snakes have two reproductive modes: oviparity and ovoviviparity. So for the giant arboreal or aquatic snake, is the python viviparous or ovoviviparous? According to available information, oviparity means directly laying eggs, while ovoviviparity means that after fertilization the eggs are not expelled but are incubated inside the body. Pythons are ovoviviparous; so-called ovoviviparity means there are eggs inside the belly, and they hatch directly inside the belly, so the small snakes we see come directly out of the mother's belly, with no eggs. Snakes of the family Colubridae are all oviparous. Pit vipers and sea snakes (with 16 genera and 55 species) are ovoviviparous snakes; among the Pythonidae, Typhlopidae and Elapidae, some are oviparous and some are ovoviviparous. As for pythons, the peak breeding rate is from late April to late May; they are oviparous, and the female lays 12 to 50 eggs each time. The eggs are white and weigh about 30 grams. The female python has the habit of coiling over the egg pile; at this time she does not eat, her body generates heat, and her body temperature rises by several degrees compared with usual, which is beneficial to the incubation of the eggs.

Ovoviviparous snakes have completely freed themselves from dependence on land and have difficulty moving or cannot move on land. Snakes that usually live in cold regions and high mountains are mostly ovoviviparous, such as the anaconda. 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 outside changing environment.

Almost all sea snakes are also ovoviviparous, and the red-banded snake and the rattlesnake are also ovoviviparous. Their fertilized eggs grow and develop inside the mother snake's body, but the embryo and the mother have no direct connection; the substances stored in the egg are the only source of its nutrition, which is fundamentally different from true viviparity. But there are exceptions: two kinds of snakes in Australia have embryos that can obtain nutrition from the mother, somewhat like viviparity. Pit vipers, bamboo pit vipers, true vipers and most sea snakes are ovoviviparous snakes. Some snakes directly give birth to small snakes, which can be called viviparous, but this differs from the true viviparity of mammals: their fertilized eggs develop in the mother snake's oviduct, but the nutrients needed for the embryo's development come from the yolk of the fertilized egg, not through the umbilical cord from the placenta absorbing the mother's nutrients, so it is also called ovoviviparity.

Appendix: Ovoviviparity (also called pseudoviviparity) refers to a reproductive mode in which the animal's eggs develop into new individuals inside the mother's body before being produced from the mother's body. However, the nutrients needed during development still rely on the yolk stored in the egg itself, with no material exchange relationship with the mother, or only gas exchange and very little nutritional connection with the mother in the later stages of embryonic development. It is a reproductive mode between oviparity and viviparity. Pit vipers, sea snakes and viviparous lizards, copper skinks, sharks, crabs, guppies and so on are all ovoviviparous animals. In addition, certain lizards distributed on the Qinghai-Tibet Plateau in our country are also ovoviviparous in the high-cold environment; this is the result of the animals' long-term adaptation and a reproductive mode formed by the animals' long-term adaptation to adverse environments.

Ovoviviparity means “incubating eggs inside the body”, that is, the fertilized eggs produced by internal fertilization in the animal remain in the mother's reproductive tract and develop into young using the yolk material of the egg itself, and are only born after the embryo has 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 appropriate protection from the mother, and the survival rate of hatching is better guaranteed than that of oviparous ones. During the development of the fertilized egg, in addition to using the nutrients of the yolk, the gas exchange and water retention needed for its development still depend on the mother's supply. Common ovoviviparous animals include some sharks, guppies and mosquito fish, as well as certain venomous snakes (such as pit vipers and sea snakes) and viviparous lizards, copper skinks and so on, all of which are ovoviviparous animals.