Slow lorises are adorable but they bite with flesh-rotting venom
By Rachel Nuwer
With their bright saucer eyes, button noses and plump, fuzzy bodies, slow lorises — a group of small, nocturnal Asian primates — resemble adorable, living stuffed animals. But their innocuous looks belie a startling aggression: They pack vicious bites loaded with flesh-rotting venom. Even more surprising, new research reveals that the most frequent recipients of their toxic bites are other slow lorises.
“This very rare, weird behavior is happening in one of our closest primate relatives,” said Anna Nekaris, a primate conservationist at Oxford Brookes University and lead author of the findings, published in Current Biology.
Researchers are just beginning to untangle the many mysteries of slow loris venom. One key component resembles the protein found in cat dander that triggers allergies in humans. But other unidentified compounds seem to lend additional toxicity and cause extreme pain.
Strangely, to produce the venom, the melon-sized primates raise their arms above their head and quickly lick venomous oil-secreting glands located on their upper arms. The venom then pools in their grooved canines, which are sharp enough to slice into bone.
“The result of their bite is really, really horrendous,” Nekaris said. “It causes necrosis, so animals may lose an eye, a scalp or half their face.”
To get to the bottom of how slow lorises use their venom in nature, Nekaris used radio collars to track 82 Javan slow lorises, a critically endangered species in Indonesia. Like other types of slow lorises, Javan slow lorises form long-term mating pairs that occupy small territories containing one or several gum-producing trees.
Over an eight-year span, the researchers spent more than 7,000 hours monitoring their study subjects in a 2-square mile patch of forest. They recaptured the animals every few months for health checks.
Shockingly, across all captures, 20% of slow lorises had fresh bite wounds — oftentimes severe, flesh-rotting injuries that entailed a lost ear, toe or more. Males suffered more frequent bites than females, as did young animals dispersing from their parents’ territories. While necrotic wounds were a regular occurrence, predation was not; since 2012, the researchers have lost just one Javan slow loris to a predator, which was a feral dog.
Nekaris and her colleagues concluded that slow lorises are remarkably territorial and that they frequently use their venom to settle disputes.