Snakes are elongated¹, legless, carnivorous reptiles² that can be distinguished³ from legless lizards⁵ by their lack of eyelids⁶ and external ears. Many species of snakes have skulls⁷ with several more joints⁸ than their lizard⁴ ancestors, enabling them to swallow prey⁹ much larger than their heads with their highly mobile jaws¹⁰. To accommodate their narrow bodies, snakes' paired organs (such as kidneys) appear one in front of the other instead of side by side, and most have only one functional¹¹ lung.

 

Living snakes are found on every continent except Antarctica, and on most smaller land masses; exceptions include some large islands, such as Ireland, Iceland, Greenland, the Hawaiian archipelago, and the islands of New Zealand, and many small islands of the Atlantic and central Pacific oceans. Additionally, sea snakes are widespread throughout the Indian and Pacific Oceans. More than 20 families are currently recognized. They range in size from the tiny, 10.4 cm (4.1 in)-long thread snake to the reticulated python of 6.95 meters (22.8 ft) in length. The fossil species Titanoboa cerrejonensis was 12.8 meters (42 ft) long. Snakes are thought to have evolved from either burrowing¹² or aquatic¹³ lizards, perhaps during the Jurassic period.

 

Venom¹⁴ 毒液

Most species are nonvenomous and those that have venom use it primarily to kill and subdue¹⁵ prey rather than for self-defense. Some possess venom potent¹⁶ enough to cause painful injury or death to humans. The colloquial¹⁷ term "poisonous snake" is generally an incorrect label for snakes. A poison is inhaled¹⁸ or ingested, whereas venom produced by snakes is injected into its victim via fangs¹⁹. It is worthwhile noting that certain birds, mammals, and other snakes (such as kingsnakes) that prey on venomous snakes have developed resistance and even immunity²⁰ to certain venoms²¹. Nonvenomous snakes either swallow prey alive or kill by constriction²².

 

Feeding and diet 饮食

All snakes are strictly²³ carnivorous, eating small animals including lizards, frogs, other snakes, small mammals, birds, eggs, fish, snails²⁴ or insects. Because snakes cannot bite or tear their food to pieces, they must swallow prey whole. The body size of a snake has a major influence on its eating habits. Smaller snakes eat smaller prey. Juvenile²⁵ pythons might start out feeding on lizards or mice and graduate to small deer or antelope²⁶ as an adult, for example. After eating, snakes become dormant²⁷ while the process of digestion²⁸ takes place.

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