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. Why does a snake possess the capability to kill hundreds of thousands of mice with each bite? This is especially odd when you consider what an expensive weapon venom is.

A single bite from a taipan snake contains enough venom to kill 250,000 mice

Venom tends to contain mixtures of protein-based toxins, often acting synergistically to wreak havoc on internal organs. A snake haemotoxic venom might contain one component that prevents blood from clotting, and another that breaks down the walls of blood vessels. The results are predictably messy.

Protein synthesis requires a substantial energy investment, but this has not stopped the evolution of venoms containingthousands of peptides and proteins, at considerable cost to the animals in question.

And to some extent, venomous animals actually account for these costs. It is difficult to test such things directly, but it appears that snakes adjust the amount of venom they injectdepending on the size of their prey, so as not to waste it.

Furthermore, one experiment conducted with pit vipers demonstrated an 11% increase in metabolic activity following venom extraction, indicating a link between physical exertion and venom production.

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