It’s always dehydrated, and it's not a great swimmer, but it can somehow cross oceans.
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.