Snakes seem like they should be some of the most awkward animals on earth, don’t they? They have no legs! And yet they are able to glide across the planet with ease and grace, and thrive in a world where having legs is not only fashionable, but useful. That’s why snakes have always impressed me. Still, there is a subfamily of snakes that found the challenge of a legless life on land too much for them. So, they went back to the ocean, where life presents its own set of difficulties, most of which these snakes have met admirably and creatively.
Sea snakes are a subfamily of the family Elapidae, which is comprised of venomous snakes. Sea snakes are found in the Pacific and Indian Oceans, preferring to live in warm tropical waters. Most are found in shallow areas, such as by coasts, islands or coral reefs.
Sea snakes can get pretty large, with most species growing to almost five feet in length, and the largest sea snake reaching almost ten feet. In order to live in the oceans, the sea snake has developed a number of wonderful adaptations that make ocean life a breeze. Firstly, sea snakes have a laterally flattened tail, which makes swimming much easier for these guys. Some even have somewhat flattened bodies, which means these snakes don’t really have scales on their stomach – something which means these snakes cannot move on land. Only one genus of sea snakes still has big stomach scales, and they still spend a fair amount of time on land.
The second big set of adaptations sea snakes have is focussed on breathing. Breathing is pretty important, I hear. Sea snakes do not have gills, so they have to surface to get the air they need. These snakes have nostrils on the top of their nose, so only a portion of their head needs to be out of the water to breathe. The nose also has tissue inside that prevents water from coming in the nostrils, and the snake can bring its windpipe to the roof of its mouth. This connects the windpipe to the nasal passage, preventing water from entering the lungs as the snake breathes. Some sea snakes can also breathe through their skin, and it has been shown that almost a quarter of the snake’s oxygen requirements can be met through skin respiration.
Sea snakes have two final characteristics that allow them to survive in the ocean. One involves salt excretion – as you can imagine, snakes that live in the ocean ingest quite a lot more salt than those on land, both through their diet and by swallowing sea water. Sea snakes have adapted to expel this salt by ‘spitting’ it out when they stick out their forked tongues to smell the water. The other adaption is that some species of sea snake have photoreceptors on their tails. It is suggested that this helps the snake hide completely in coral reefs, as the snake can detect if its tail is sticking out.
Being part of Elapidae, most sea snakes have very potent venom. Luckily, however, fatal bites from sea snakes are fairly rare, for two reasons. One, they are usually quite shy and timid animals, who would rather hide than bite someone. Two, when they do bite, very little venom is actually injected. Still, you should never provoke a sea snake, and definitely stay away from them on land, as they tend to flail about and bite anything within their reach.
So there you have it, the story of how some snakes decided land was too difficult for them, so they went out to sea. Turns out living in the ocean is also pretty hard, but I guess the snakes were too embarrassed to go back onto land, so they sucked it up and made a life for themselves. Pretty cool, right?
Cover image source: http://tvblogs.nationalgeographic.com/2010/11/11/hunting-for-snake-venom/