Why some animals have venoms so lethal, they cannot use them

Why some animals have venoms so lethal, they cannot use them 

We have all heard stories about snakes, jellyfish and scorpions that can kill humans. But why have these animals evolved such toxic venoms, when they are of so little use?

 My reverie as I walk through Costa Rica’s beautiful Corcovado National Park is brought to a sudden halt when the guide’s arm slams into my chest. “Stop!” he shouts, pointing at something thrashing around in the sand. “Sea snake.”

As I watch the yellow-bellied sea snake, out of its element and seemingly distressed, a piece of trivia from my childhood surfaces in my brain. Read more.