These gutsy rats bathe themselves in deadly poison to ward off predators

Transcript

Most rats are known for scurrying away in the face of danger. But the African-crested rat prefers to stand its ground.

That's because, unlike your average rodent, these fluffy little critters are literally bathed in a deadly poison. 

"Instead of necessarily always running away really quickly, they will stop and display and sort of make the signal like, 'You really don't want to mess with me. I don't need to move very fast because it's you who should be backing off,'" biologist Sara Weinstein told As It Happens host Carol Off.

"They certainly have the, in my opinion, the behaviour of something that knows it's poisonous but knows it's defended."

Weinstein, who works with University of Utah and the Smithsonian Conservation Biology Institute, has been studying the creatures along with her colleagues since 2018. Their findings were published last week in the Journal of Mammalogy.

A toxic bath 

Folks who live in East Africa have long known the African-crested rat is poisonous. It's felled more than a few hungry dogs over the years. 

But its poison is not its own. Instead, the resourceful creature makes use of the deadly toxins found in poison arrow trees.

"They chew up the bark in the leaves, and they mix it in with their spit, and then they sort of just turn around and groom it into their fur. So they're just using their mouth to lick and chew it into these specialized hairs," Weinstein said.

"If you were to look at one of these poison hairs, they're actually almost like a honeycomb in structure. So they've got all these crypts and holes in them and that actually wicks up spit poison plant mixture."

The poison plant bath makes the African-crested rat the only known toxic rodent. 

And when facing down a predator, the rat will puff up that special fur, displaying the black and white stripes that give the species its name. 

The New York Times described the African-crested rat as resembling "the love child of a skunk and a steel wool brush," but Weinstein says they're "much cuter than than, you know, any progeny of a steel wool brush would ever be."

Weinstein and her colleagues didn't discover the phenomenon. It was first documented in a 2011 study based on observations of a single rat.

"We really wanted to confirm that finding and expand on it a little bit more. So in our work, we're able to document this behaviour in many more animals, and able to show that the animals could chew on this incredibly poisonous plant that, if we were to chew on, we would get very sick, potentially even die," Weinstein said.

"The rats can chew on this and they're absolutely fine. They do this, then they go on with their normal rat behaviour."

Asked how the rats are able to chow down on deadly poison arrow trees without getting poisoned themselves, Weinstein said: "That is the million dollar question."

Now that they've confirmed the behaviour, figuring out how it works is the next step. But she says they have a few theories.

They could have mutations to their sodium potassium pumps, which is where the poison binds. Or they might have a specialized gut microbiome that breaks the poison down. Or they could have liver enzymes that help detoxify the compounds.

"There's lots of potential areas to look now, and it may actually be a suite of a bunch of different adaptations that play a role," Weinstein said.

The researchers made some other discoveries about the African-crested rat in the course of their observations. 

For example, while they may be intimidating to anything that likes to snack on rodents, they're actually pretty sociable with each other. 

"One of the more remarkable things we actually discovered as part of this research was that these large rodents, which would generally be assumed to probably be solitary, actually probably aren't," Weinstein said.

"We assumed that they were probably, you know, living alone. But as we started trapping and actually observing their behaviour, we got some evidence that they may actually potentially be monogamous or live in male-female pairs or even small family groups, at least for part of the year."

Written by Sheena Goodyear. Interview produced by Kate Swoger.