The African crested rat is the only mammal in the world known to make use of a lethal plant toxin for its own defense, according to a multinational team of researchers from England, the U.S. and Kenya.
The giant 14-inch (36cm) long rat can incapacitate and even kill large predators by utilizing the same plants that African tribesmen use for poisonous arrows. The rodent has been seen killing local dogs, but, up until now, researchers did not have a clue how.
It seems after chewing the "poison-arrow plant," the African crested rat stores its poison-laced spit in specially hollow hairs in its mohawk that it then uses when a predator attacks. Upon sensing a threat, the rat will sting its attacker with the poison and spit-tipped hairs, which can sicken and kill the enemy.
Hunters have used poison from the tree's bark for thousands of years to hunt prey as large as elephants. However, what's amazing is that these rats don't die when they chew the poison.
"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," said study researcher Jonathan Kingdon of Oxford University in England.
"This is the first mammal that is borrowing a deadly poison from a plant and slathering it on itself without dying," Kingdon added. "This is an extraordinary thing to have evolved."
When the rat is threatened, it arches its back and uses specially adapted muscles to slick back its hair and expose a strip of poison. While the poison can be lethal, Kingdon argues that it is not to the rat's advantage to kill the animal.
"If it killed every time, nothing would ever learn that this is distasteful. The way it really works is that you go away and you recover from a terrible experience and you never, ever invite that experience again."
They team tested the chemicals in the hairs' poison along with the bark of the Acokanthera schimperi, which the rats were known to chew.
Kingdon grew up in Africa and even kept an African crested rat as a pet as a child. He heard rumors that the rodent was poisonous, but it took him 30 years to figure out why.
He and his colleagues studied the rats in the wild as well as in a lab where they ran tests on a line of hairs along the rodent's back. What they found, was a unique structure.
The rat's hair is unlike any other. It is specifically adapted to absorb the poison with an outer layer full of large holes (like a pasta strainer) and an inside that is full of straight fibers to wick up the liquid.
While much was learned in the study, the mystery remains: Why don't the rats die from the poison?
"The rats should drop dead every time they chew this stuff but they are not," Kingdon said. "We don't have the slightest idea how that could be done."
"A poisonous surprise under the coat of the African crested rat" was published in the August 2 journal Proceedings of the Royal Society B: Biological Sciences.
You can read more about the study to see how scientists hope to learn about how the poison works and what makes the rats resistant. It could hold the key to unlocking medical mysteries in humans as a similar chemical, digitoxin, has been used for some time to treat heart failure.