Why they're dangerous: These spear-equipped swimmers mostly live in the ocean, but you do find them in fresh water in Southeast Asia and the Amazon. "They are probably the most feared fish in South America," says Wade. "If you step on them, they will take exception and stab you in the foot or lower leg. By all accounts, it's incredibly painful. It's a sharp blade: serrated down the sides and covered in toxic, necrotic venom. It makes a very messy, dirty wound." Though not usually fatal, a sting can lead to complications if left untreated. "Worst case, it can get gangrenous and you might have to amputate the leg," he says, adding, "well, very worst case, I've heard stories of children who get stabbed in the abdomen. That can be fatal in a short period of time."

How to stay safe: Don't step on them. This can be difficult, since they're often buried in mud. But locals can show you how to do what's called the "stingray shuffle." "Instead of picking your feet up and planting them down, you do shuffle them forward," says Wade. "That way you're going to sort of nudge the edge of the stingray, in which case it will probably just flutter away. It will make them aware that you're there without actually having trodden on them."