When venom is too powerful

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? facebook

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.

"Sea snakes," my younger self reminds me, "are the most dangerous snakes of them all. You should be careful."

True enough, many sea snakes - and land snakes for that matter - are incredibly venomous. A single bite from a taipan snake contains enough venom to kill 250,000 mice, for instance. And it is not just snakes that hold this sort of power. One drop of marbled cone shell venom can kill 20 humans. A box jellyfish sting can cause cardiac arrest and death in a matter of minutes.

This begs the question: why possess a weapon powerful enough to kill dozens if you are only ever going to use it in a one-on-one situation, and specifically if you have no intention of hunting anything the size of a human?

It is reminiscent of the commonly held myth (and it is a myth) about daddy longlegs; namely, that they possess the most powerful venom known to man, but evolved it for nothing because they lack the means to administer it. The most powerful venoms just seem to make no evolutionary sense.

The reason for an animal possessing toxic weaponry is simple enough. Venom is a means by which to subdue prey without risking your own neck in the struggle. Secondarily, it is also a useful defensive strategy. What is strange, however, is the level of venomous excess found in nature.

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