This Monogamous, Poisonous Rat Is Full of Surprises

This Monogamous, Poisonous Rat Is Full of Surprises
A pair of African crested rats. (Image: The University of Utah)

Looking like a cross between a ferret, a skunk, and a porcupine, the African crested rat may be adorable, but it packs a poisonous punch. New research explains the remarkable way in which these mammals acquire their toxin, and how these rats — once thought to be loners — tend toward monogamous relationships and even family units.

They’re cute, no doubt, but you wouldn’t want to snuggle up with one of these things. The African crested rat (Lophiomys imhausi) slathers its fur in a deadly toxin. This poison is no joke, as just a few milligrams can bring an elephant to its knees and even kill a human, according to a statement put out by the University of Utah.

That the crested rat is dangerous shouldn’t come as a surprise, given its audacious, skunk-like appearance — a warning to would-be predators to back the hell off. When these rats sense a threat, the hairs on their back stand erect to form a prominent crest, hence their name. This posture allows the rabbit-sized animal to further intimidate its enemies.

An African crested rat (omg look at those adorable little hands).  (Image: The University of Utah) An African crested rat (omg look at those adorable little hands). (Image: The University of Utah)

We’re learning more about these rare creatures thanks to new research published in the Journal of Mammalogy. Biologist Sara Weinstein from the University of Utah, along with her colleagues from the National Museums of Kenya and the Smithsonian Conservation Biology Institute, uncovered new evidence affirming the method used by these animals to source the poison, which they do by extracting it from the poisonous arrow tree. The new research also yielded some unexpected findings about their behaviours. The crested rat is not a solitary animal, as presumed; they appear to be monogamous and even family oriented, forming small units with their offspring.

A research paper from 2011 announced something that folks in Kenya had known for a long time: These rats are poisonous. The study claimed that crested rats acquire their toxins from the poison arrow tree (Acokanthera schimperi), which humans traditionally use to source toxins for poison-tipped arrows. These plants contain cardenolides — toxic compounds akin to those found in monarch butterflies and cane toads. Monarch butterflies, which are poisonous, acquire cardenolides by ingesting milkweed, while poisonous cane toads have special glands that produce the chemical. The crested rat is more like the monarch butterfly in that it must source the poison externally. To suddenly become toxic, the rats chew bark from the poison arrow tree and then lick the deadly chemical onto their specialised hairs.

A major deficiency of the 2011 paper is that the poison sequestration behaviour was limited to the study of one individual. For the new research, the scientists sought to learn more, relying on camera traps and analysing and observing captured critters.

The team set up 35 camera traps in central Kenya, which monitored free-roaming rats from March to September 2018. The cameras struggled to detect their movements, as the crested rats move slowly through their environment. In future, “mapping their range and habitat preferences will require carefully designed and targeted surveys,” wrote the authors in their paper.

Camera trap image showing a lone crested rat. (Image: S. B. Weinstein et al., 2020/Journal of Mammalogy) Camera trap image showing a lone crested rat. (Image: S. B. Weinstein et al., 2020/Journal of Mammalogy)

More excitingly, the researchers managed to capture 25 individuals. This was an extraordinary number, given how rare these creatures are, but also because they’re exceptionally difficult to trap. Using aromatic foods like fish, peanut butter, and vanilla seemed to do the trick.

With close-up access to the animals, the researchers determined their sex and weight, gathered faeces, tissue, and hair samples, and placed tags on their ears (the scientists wore leather gloves to avoid contact with the poison). Most of the captured rats were released back into the wild, and the methods used were in accordance with the American Society of Mammalogists guidelines on the ethical treatment of research subjects.

Ten rats were taken to a nearby research station. And by research station, we’re talking about an abandoned cow shed. Inside this makeshift facility, the researchers did their best to simulate the rats’ natural habitat in tree cavities by building stalls fitted with tiny ladders and nest boxes. Using cameras, the team gathered 447 daytime and 525 nighttime monitoring hours, during which they documented many of their behaviours.

“They’re herbivores, essentially rat-shaped little cows,” Weinstein explained in the statement. “They spend a lot of time eating, but we also see them walk around, mate, groom, climb up the walls, sleep in the nest box.”

The animals displayed many social behaviours during their time in captivity.  (Image: S. B. Weinstein et al., 2020/Journal of Mammalogy) The animals displayed many social behaviours during their time in captivity. (Image: S. B. Weinstein et al., 2020/Journal of Mammalogy)

The animals were monitored as individuals, pairs, and groups. One of the more revealing observations came when a female was paired with a male captured at the same site. African crested rats, as the new research suggests, are monogamous.

“We put these two rats together in the enclosure and they started purring and grooming each other,” said Weinstein. “Which was a big surprise, since everyone we talked to thought that they were solitary. I realised that we had a chance to study their social interactions.”

Interestingly, large juveniles were captured in locations inhabited by adult pairs. This suggests they stay with their parents for an extended period. Further observations in the cow shed, er, research station, showed that paired rats liked to spend their time next to each other, and they often followed each other around.

With their baseline behaviours established, the researchers presented the animals with branches of the poison tree. Most of the time they couldn’t be bothered, but 10 individuals did take the time to chew on the branches, slosh the mush around their mouths with spit, and then lick it onto their specialised hairs. As the paper points out, “chewing on A. schimperi and cardenolide exposure had no effect on feeding, movement, or total activity.” The crested rat, it would appear, has developed a tolerance for the poison. That the animals didn’t immediately jump at the opportunity to sequester poison from the branches is a possible indication that the toxin lingers on their hairs for a long period of time, which is known from the use of poison on arrowheads.

Looking ahead, the researchers would like to learn more about their behaviours and population size. The IUCN currently lists the species as being of least concern, but the team would like to learn more just to be sure. As the IUCN points out, conservation actions are needed to maintain the rats’ current status. In addition, the team would like to raise the public’s awareness about this remarkable creature. I for one would certainly like to learn more about these menacing little oddballs.

[Video credit: Sara B. Weinstein (2020). The Smithsonian Institution.]