As if the idea of giant rats wasn’t freaky enough, a group of scientists have confirmed that the African crested rat, a rabbit-sized rodent, can lace its fur with poison deadly enough to fell an elephant.
Collaborative work across the Dearing Group, National Museums of Kenya and The Smithsonian discovered that not only is this the only mammal to store plant toxins for future, but that it does so by chewing on poisonous plants. Native to East Africa, the rat's resistance to these toxins is still to be investigated.
Researchers didn't know how these rats became so poisonous for the first time. By creating a rat enclosure, they discovered the little critters chew poisonous plants to draw out the toxin. The rats then lick and chew the poison into specific regions of their fur. Microscopic images reveal differences in poisonous patches of fur by comparing single hairs of “normal” and “poisonous” fur.
When threatened or excited, these crested rats can flare their fur. Skunk-like black and white racing stripes become more visible, within which lies their secret defence.Unlike skunks, the rats do not spray the toxins instead warding off attack with anti-predator behaviour.
Describing this defence, Dr Sara Weinstein, lead author of the paper and disease ecologist at the University of Utah, explains that an attacking animal is “a mouthful of these really potent toxins”, which can lead to death, or sickness in animals. Predators which survive will look elsewhere, fearful of this particular fur-ball.
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This defensive behaviour had only been studied in one rat before, but now Dr Weinstein and her colleagues have studied 25. “The patterns we were seeing were able to see in many individuals proved it wasn’t just a freak occurrence," she said. "We know that this is behaviour that they seem to do consistently.”
Offered different plant branches, the rats tended to coat themselves with cardenolides (bitter, heart-arresting toxins) found in the A. schimperi plant. Acting selectively, they didn’t always interact with the plants when offered, sometimes sniffing and nibbling here and there without coating their fur. They may be judging how harmful the poison could be with their keen sense of smell.
With more to explore, including surprising social interactions between the rats, the collaborative work will continue. Weinstein shares that there remain “so many questions” and looks forward to further work by herself and other great scientists.
Future work will investigate both behavioural and biochemical factors of these intriguing creatures. Using DNA sequencing, we could learn how African crested rats (and even their fleas) remain unaffected by this poison. Studying their social structures could reveal new information about the rats’ relationships.
For now at least – be wary of fluffy, rabbit-like animals in the wild. Weinstein warns that while they “look cute”, their distinctive fur flaring of the African crested rat makes for a potent pet.
Reader Q&A: Can wild animals become overweight?
Asked by: Meghana Vipin
In 2019, firefighters in the German town of Bensheim rescued a chubby rat that had become stuck trying to squeeze itself through a small gap in a manhole cover. The rotund rodent was sent on its way with a valuable life lesson: that overeating isn’t necessarily a good idea.
Overweight animals are slow and vulnerable to predation, so don’t last long. The animals we think of as fat – seals, walruses and polar bears – aren’t overweight at all. Their blubber is an adaptation that offers buoyancy, insulation and energy storage, so sometimes it’s all about survival of the fattest.
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