Giant African Rat Kills with Poisonous Mohawk

The African crested rat has been known to kill local dogs, but researchers have just figured out how. After chewing the "poison-arrow plant," the oversized rodent stores its poison-laced spit in special hollow hairs in its mohawk. Then, when a predator grabs the rat, the animal gets stung with the poison and spit-tipped hairs that can sicken and kill.

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

Kingdon grew up in Africa and was frequently exposed to these rats, even keeping one as a pet.  While he had always heard that the rodent was poisonous, it took 30 years for him to figure out how.

Essentially, whenever a predator, such as a dog, comes upon the rat and tries to ingest it, the animal gets a mouthful of potentially lethal poison.

However, Kingdon argues that it isn't to the rat's advantage to kill the animal. It has a different approach: "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."

Kingdon and his colleagues studied the rats both in the wild and in the lab where they ran tests on a line of hairs that run along the 14-inch (36cm) long rat's backs. They found that it had a unique structure, so they also tested the chemicals in the hairs' poison alongside that of the bark of the Acokanthera schimperi, which the rats were known to chew.

Hunters have used poison from this tree bark for thousands of years to hunt prey as large as elephants.

The researchers found that the rats chew the bark of the poisonous tree and lick themselves to store their poisonous spit in specially adapted hairs. It's a trait that appears hardwired into the rodent's brain.

"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.

When threatened, the rat arches its back and uses specially adapted muscles to slick back its hair and expose the strip of poison.

Perhaps the most shocking find -- and the one that is the most beneficial to scientists -- is that the structure of the rat's hair is unlike any other. It is specially designed to absorb the poison with an outer layer full of large holes and an inside that is full of straight fibers to wick up liquids.

The biggest mystery remains: Why don't these rats die from chewing 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."

Learning more about how the poison works and how the rat is resistant could be a boon to human medicine, since it acts by inducing heart attacks. A similar chemical, digitoxin, has been used for decades to treat heart failure.

The study, "A poisonous surprise under the coat of the African crested rat," was published on Aug 2 in the journal Proceedings of the Royal Society B: Biological Sciences.  To learn more, CLICK HERE