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Rats with poisonous hairstyles live surprisingly sociable private lives

Crested rats not only chew the bark of trees poisonous enough to kill an elephant. Rabbit-sized rodents dribble and lick the toxic drool in their long rat fluff for an armed hairstyle. However, these dangerous rats, which scientists assumed were solitary, turn out to have a close and cuddly family life. They even purr.

Chewing the bark or other parts of the poisonous arrow trees of East Africa gives the rats toxic saliva to apply to specialized areas of skin. The toxins sink into porous, easily separable hairs on the flanks of the rat. Any predator crazy enough to bite a Lophiomys imhausi gets a furry bite of bitter toxins that human poachers use on the arrows to hunt larger game.

Rats “have the personality of something poisonous,” says ecologist Sara Weinstein, who studied them during a Smithsonian fellowship at Kenya’s Mpala Research Center. "They can run fast if they feel like it, but they usually don't." Rats are more likely to walk away from problems or stand firm, whistling, growling and growling.

Catching crested rats conducted some experiments, says ecologist Katrina Nyawira, who worked on the project with Weinstein before moving to Oxford Brookes University in England. "Sometimes we cheated for about two weeks and we only got one individual and, trust me, that would be a win."

Sara B. Weinstein (left), Katrina Nyawira (right) are in a poisonous African arrow tree, which provides defensive toxins to crested rats.Stephanie Higgins

Researchers set traps in a strange variety of places, from remote places in the Kenyan savannah to the door of someone’s room, Nyawira and Weinstein realized that the common success factor was access to arrow poison trees (Acokanthera muvperi).

With bright green leaves in the shape of drops of fat tears, this tree of extended shade is a cousin of American dairies that give monarch butterfly caterpillars their defensive toxins. From roots to shoots, the arrow poison tree carries potent cardenolides that can give heart attacks to potential predators.

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When Weinstein and Nyawira trapped a crested rat for a few days of video observation, the researchers shoved some fragments of the deadly bark of the trees and roots into the temporary cages. The cameras occasionally caught a nocturnal rat touching its poisonous hair. Instead of disguising themselves in the toilet, the animals overcame the handling of the poison in 10 minutes.

Weinstein wondered if the 25 animals they caught paid any price for licking toxins: "Do they get sick and have to take a nap to sleep?" However, the videos did not show additional naps, or slowness, or other noticeable changes in behavior after hair care. For crested rats, the venom can actually be just mousse.

How these rats endure things is an ongoing mystery, with much speculation. The stomach of this species, for example, has more cameras “like a cow … than the typical pizza rat,” says Weinstein, now at the University of Utah in Salt Lake City.

He hadn’t thought about studying the domestic life of crested rats, but a whim why he hadn’t changed it. Weinstein once again set a trap in the same spot where he had just caught a crested rat. He had heard that the rats were lonely, so his first catch should empty the territory. However, he quickly caught a second rat in the same place.

"We put the two rats next to each other," Weinstein says, "They start purring, this vocalization we've never heard before."

“They looked a lot like they wanted to be together,” he recalls. One was male, the other female. When Weinstein allowed the rats to enter the same cage, the two began to prepare. One began to follow the other and the couple retired to the private retreat of the cage, a nest box.

Over several months, Weinstein and Nyawira eventually captured four more male-female pairs. Two couples had boys and each family grouped together when they were reunited in captivity. In videos, members of the couples stayed close, spending about half the waking time just 15 inches apart, investigators reported Nov. 17 online in the Journal of Mammalogy.

The videos inside the nest box looked especially cozy. Pairs grouped in strips of nose fluff to the tail "like a big scarf," says Nyawira. Her hair is "very soft, like cat skin." Or as Weinstein says, "They're super cute."

The unusual crested rats of East Africa are not the lone facts the scientist expected. Rats are best known for chewing the bark or other parts of a poisonous tree and dribbling toxic saliva on their skin. Any potentially crazy predator to bite receives a life-threatening bite of detachable lint that can induce a heart attack. But rats with these dangerous hairstyles look good domestic. The cameras reveal that they cling close to a partner and crouch down to sleep in a mutual cloud of fluff.

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