Animals have lots of options for thwarting potential predators. Some run away, some hide, and some use sharp teeth, long tusks, or claws for fighting. Others are poisonous: eating or touching them results in illness or death. Most animals make their own poison. But some borrow their poison from animals in their diet.

Poison frogs of the family Mantella, living in Madagascar, do just that. So do the South American frogs of the families Dendrohates, Phyllobates, and Epipedobates. Frogs from all four of these families get their poison from eating poisonous ants. The ants are high in alkaloids, a strong, nastytasting chemical. When other animals eat the ants, they spit them right out, but the members of our four frog families gobble them up.

Why aren't the frogs affected by the ants' poison? They have evolved over hundreds of thousands of years to be resistant to the alkaloids. There are myriad such examples in the animal kingdom: birds can pick off poison spiders, snakes eat poison toads, and fish eat venomous worms. What's more amazing than being able to withstand the poison is that the frogs have evolved a way to use it. Most of the insects they eat are non-poisonous, but when they happen to eat a poison ant, they are able keep the alkaloids from passing through their system and out the other end like any other rejected food waste. They keep the poison in their bodies and concentrate it where predators would taste it first: in their skin.

Most amazing of all is that the poison frogs in Africa and South America are not related to each other, and the ants they eat are not related to each other. Over millions of years, ants living on the two separate continents evolved to use alkaloids as a poison; then frogs evolved on each continent thai could not only eat these ants but could steal that poison for themselves. Finally, the two groups of frogs both evolved bright coloration, as a warning to predators.

This is what biologists call convergent evolution: different groups independently develop the same solution to a problem. In other words, it's a random process that looks pretty clever.

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