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Biologists Explain How An African Rat Makes Itself Poisonous

East Africans have always known that crested rats are poisonous. They know that the dogs that tend to attack the foot-long mammal end up viciously sick and deathly scared of the creature.

As Science , the publication of the American Association for the Advancement of Science, explains it, another thing that made the rat unique is that instead of running from predators it faced them:

... They twist to the side and arch their backs, parting their long, gray outer coats, to reveal black-and-white bands that run like racing stripes down their flanks. Like a hornet's yellow-and-black rear or a rattlesnake's rattle, these stripes seem to tell predators one thing: Back off.

The rats' defensive postures are fearsome, but they don't explain the trails of sick dogs left in their wakes. Researchers suspected that the rodents were harboring poison, but they didn't know how.

In a study published in Aug. 2 edition of the journal Proceedings of the Royal Society B: Biological Sciences,scientists explain that the rats coat their fur with the same poison African tribesmen used to take down large prey like elephants.

When a predator bites, they get sick and never again come after a rat.

One of the authors of the study told MSNBC that the behavior is an evolutionary marvel.

"This is the first mammal that is borrowing a deadly poison from a plant and slathering it on itself without dying," Jonathan Kingdon, of Oxford University in England told MSNBC. "This is an extraordinary thing to have evolved."

And here is their explanation for how the rat does it:

They found that to make its poison fur, the rat — which averages about 14 inches (36 cm) long — chews the bark of the A. schimperi and licks itself to store the resulting poisonous spit in specially adapted hairs. This behavior is hardwired into the animal's brain, similar to nitpicking behavior of birds or self-bathing of cats, the researchers suspect.

"What is quite clear in this animal is that it is hardwired to find the poison, it is hardwired to chew it and it is hardwired to apply it to the small area of hairs," Kingdon said. The animals apply the poisonous spit only to the specialized hairs on a small strip along its back. When threatened, the rat arches its back and uses specially adapted muscles to slick back its hair and expose the strip of poison.

The researchers provided this video of a rat in captivity exhibiting the behavior:

Science points out that other vertebrates "spirit away toxins from plants and other animals," like the poison dart frog does. But the behavior is rare in mammals. But capuchin monkeys, for example, rub themselves with millipedes to repel mosquitos.

Copyright 2020 NPR. To see more, visit https://www.npr.org.

Eyder Peralta
Eyder Peralta is NPR's East Africa correspondent based in Nairobi, Kenya.