If someone asked you to think about a global animal that has spread over much of the earth, you’ll probably think of something like the brown rat, the rock pigeon, or us humans. You probably won’t think about the yellow-bellied sea snake.
It’s a striking animal—two to three feet in length, with a black back and yellow belly. And it is extraordinarily far-ranging for a snake. It lives throughout the Pacific Ocean, which is already more area than all the continents combined, and the Indian Ocean too. Of all the tetrapods—the animal group that includes mammals, birds, reptiles, and amphibians—this little-known snake is one of the most abundant and widespread.
“Off the coast of Costa Rica, there are some good days where you can observe hundreds or thousands of them over a couple of hours,” says the French scientist Francois Brischoux, who has been studying this species for a decade.
The 62 species of sea snakes are all wonderfully adapted to life in the oceans, but they almost always come ashore to lay eggs. But not the yellow-bellied one; it is the only member of the group that lives full-time in the open ocean. It eats at sea, mates at sea, and gives birth to live young at sea. It has special valves in its nose to stop water from getting in, and can even partially breathe through its skin. It hunts by sitting amid flotsam and picking off small fish that gather beneath it. And it swims by propelling itself with a flattened, paddle-like tail.