The Cute-but-Deadly Slow Loris Reserves Its Flesh-Rotting Venom for Its Peers

The world’s only venomous primates just got weirder.

A zoomed in photo of a Javan slow loris clinging to a tree branch with green leaves in the background. It's a small primate with light, golden fur. It has large brown eyes and a short snout. It clings onto the branch with all four limbs wrapped around it.
Javan slow lorises are now one of only six mammal species known to use venom against individuals of their own species. (Aprisonsan via Wikimedia Commons under CC BY-SA 4.0 International)


Slow lorises—a small group of wide-eyed, nocturnal primates found in the forests of south and southeast Asia—might look adorable, but think twice before snuggling up to one. They may look harmless, but a slow loris can pack a gnarly bite laced with venom powerful enough to rot flesh.Scientists have long been fascinated with slow lorises, and until now, they haven’t been able to pinpoint exactly why they have venom or how they use it. However, a new study suggests that slow lorises mainly use their toxic bites in fights against each other instead of defending themselves against other species, reports Liz Kimbrough for Mongabay.

“This very rare, weird behavior is happening in one of our closest primate relatives,” Anna Nekaris, lead author on the study and a primate conservationist at Oxford Brookes University, tells Rachel Nuwer for the New York Times. “If the killer bunnies on Monty Python were a real animal, they would be slow lorises—but they would be attacking each other.”

A bite from a loris is no joke. They have glands underneath their armpits that ooze noxious oil, and when they lick those glands, their saliva combines with the oil to concoct the venom. It fills into their grooved canines, which then deliver a grisly bite strong enough to pierce through bone. The imbued venom causes the victim’s flesh to rot away, and some lorises have even been seen with half their faces melted off, Nekaris tells the Times.

As the only group of venomous primates, slow lorises were already seen as oddities in the animal kingdom, and for decades, scientists debated why a primate would evolve to be venomous. They originally hypothesized that the venom was used to defend themselves from predators or to ward off parasites.

To finally uncover how lorises use venom in the wild, Nekaris and her team of researchers spent eight years studying critically endangered Javan slow lorises in Java, Indonesia. They collectively logged 7,000 hours studying the lorises’ behaviors and health; they equipped 82 lorises with radio collars to track their movements, and the team captured individuals every few months to monitor their health.

During their routine health checks, the team found that 20 percent of all the lorises had fresh bite wounds inflected by other lorises. Around a third of the females and 57 percent of the males showed signs of a bite; younger lorises also had more bites than older individuals. The team concluded that slow lorises are viciously territorial, and they use venom as their weapon of choice. Males are known to defend their mates while females are protective of their offspring and food. They really are “adorable little furballs of death,” Nekaris tells Mongabay.

Slow lorises join an exclusive group of only five other mammals known to use venom against individuals of their own species. The list includes vampire bats, two species of shrews, platypuses and solenodons, which are shrew-like critters found in Central America. Nekaris tells Mongabay that it’s rare for both males and females to have venom and also use it. In species like the duck-billed platypus, males use their venom against each other during mating season.

Very few studies provide in-depth analyses of how individuals within a species use venom to settle disputes or vie for resources, Ronald Jenner, a venom specialist at the Natural History Museum in London who was not involved in this research, tells the Times. But, he says, to his knowledge, “this is the most extensive field study ever done on this topic.”




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