Snakes are legless reptiles that propel themselves forward or from side to side by slithering their bodies in curling movements. Snakes mostly live on the ground or in trees, although some types live in the ocean or in freshwater lakes and ponds. Snakes feed on other reptiles in addition to birds and small mammals. These reptiles can be either oviparous, which means they lay eggs, or ovoviviparous, which means they fully incubate their eggs internally before giving birth to live offspring. In some families of snakes, one of these characteristics predominates, but there are exceptions.
Generally the Colubridae family of snakes consists of egg layers, although one type of Colubridae snake is an exception: the garter snake. Garters live in a variety of habitats, including being kept in captivity as pets. Garter snake mothers give live birth in mid-summer to anywhere from a few to several dozen snakes. Because they live in temperate climates and are exposed to lower temperatures, garter snakes carry their eggs internally to keep them incubated so that the baby snakes develop properly before birth.
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The Boidae family of snakes is divided into two categories based on their reproduction methods: boas and pythons. Environment can play a significant role in whether these snakes are oviparous or ovoviviparous. Pythons live primarily in tropical regions, and because of the warm temperatures of their habitats there is no environmental reason for them to incubate internally. Boas, however, are often found farther south or north of the tropics, so they are more likely to carry their eggs internally before giving live birth. Boa offspring are born in soft, leathery sacks, from which they immediately extricate themselves.
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Generally all snakes within the Viperidae family give live birth. The Viperidae family includes species such as pit vipers and rattlesnakes. These ovoviviparous snakes may carry the eggs inside their own stomachs for up to an entire year before laboring the baby snakes from their bodies. While the Viperidae family mothers gestate, they cannot eat and have trouble protecting themselves from predators. Baby vipers are generally born without mucus membrane sacks and are free to roam around immediately after birth.