Most of the animal species are born with the ability to swim, so are the snakes. All species of snake can swim, no matter the type of water. The prime reason you don’t see all snakes in your local pond but in your garden is that many species prefer land to water. Most of the snakes like to live in the dry land while some species spend their entire lives in water. It is the latter category that we usually call water snakes.
The snakes use different kinds of terrestrial locomotive techniques. At least five of the techniques have been identified, lateral undulation being the one most often used among them. All kinds of snakes swim in almost an identical way and it is highly similar to lateral undulation. This is the same mode they employ to move along a smooth surface as well. The snakes primarily use the surface tension of the water to glide along. They curve their bodies in a certain way while traveling through the water. They would swerve to one side first and then the other, and would repeat that motion. It is like they are drawing a big ‘S’ with their body continuously in the water. These undulations start at the head and continue down the length of the body. Just like the cars of a train follow the engine; their bodies would follow the movement of the head of the snakes. Each time they turn, they put force on the water behind them, and the resulting opposite momentum pushes them forward. The tail in particular serves to provide the momentum forward.
Since the water does not provide a solid platform like land, the swimming is more difficult for snakes. However, most species are adept in it. The water residents have acquired a more flattened structure through evolution to aid their movements. Some species have paddle-like tails and nostrils placed on backside to aid the movement.
Some species are better swimmers than others. Some water dwelling species can travel even for miles without stopping. There are also some differences in the swimming style of various kinds of snakes. For example, the venomous cottonmouth snakes, inhabiting the coastal plains of America, often hold their head a little above the water surface while moving. This is identified as a defensive mechanism, to sense the approach of other predators. But many other water snakes glide under the water, their head in level with rest of their body. The slightly differing swimming styles often help to identify the venomous from harmless ones.
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