In the dim light of the Duke Lemur Center in Durham, NC, Anne-Claire Fabre filmed an aye-aye named Kali eating with her hands. Fabre, an assistant professor at the University of Bern and an associate scientist at the Natural History Museum in London, had come to the center to study the evolution of grasping behavior in primates and aye-ayes, which are nocturnal primates with huge ears and graying hair. fur—they certainly have a unique grasping style. They have six fingers: three regular, one pseudo-thumband two elongated, almost skeletal middle and ring fingers.
At some point, Kali stopped eating. She extended her long, slender middle finger and began to insert it into her nose, pushing it deeper and deeper. “It was quite impressive to see,” said Fabre. “It’s fascinating that such a long finger can go so deep.” Shortly after Kali put his entire finger up her nasal cavity, she made her intentions clear with a determined lick. “The animal was eating the boogers,” Fabre said. “I could see it perfectly.”
(Warning: Video contains nose picking.)
For Fabre, Kali’s ability to fit all 3 inches of her longest finger inside her tiny skull raised some anatomical questions. “You get the sense that she’s getting into her brain, basically, but that’s not the case,” Fabre said. As he left the room, Fabre asked some of his classmates at the center if they had ever seen an aye-aye pick its nose before. Some had not. Others had, but never caught it on film. Fabre wanted to know where, exactly, her finger went. Subsequent research by Fabre and his colleagues into the aye-aye’s penchant for rhinotillexis, or nose picking, was published Wednesday in the zoology journal.
The researchers obtained a CT scan of an aye-aye specimen from a museum and then digitally created a model of the head and hand to understand how deep the finger could reach. (The researchers wisely didn’t try to scan an aye-aye in the act of pinching.) The scans revealed that the finger extended through the entire nasal passage and then descended into the pharynx at the back of the mouth, like an apocalyptic COVID test. Speaking personally, the resulting look is terrifying: a finger boldly going where no finger has gone before or should go in the future. However, the act does not seem to harm the aye-aye; Fabre said he believes the vets at the lemur center would have noticed if the primates had any kind of infection or irritation around their noses.
The middle finger of an aye-aye is a strange and remarkable tool. It sits on a ball-and-socket joint that allows it to rotate in any direction, similar to the human shoulder. Aye-ayes rely on their slender fingers to forage for food in a strategy called “percussion foraging.” Primates tap trees with their long fingers and listen for echoes from hollow areas. They then bite through the bark, unfurl their longest finger, insert it into the tree, and snag grubs and other larvae with a specialized claw, Jason Bittel wrote in Pacific Standard.
Although the long finger has clear benefits for food, it is less clear what the aye-aye gains from its mucus. The researchers examined the scientific literature on nose picking and found that bites were relatively rare. “There are so few studies on it,” Fabre said. And a lot of these studies focus on humans, with some concluding that a lot of people pick their noses but are embarrassed to admit it. In the book Consume the inedible, a chapter titled “Eating snot. Socially unacceptable but common: Why? he suggested that humans pick their noses because of the texture, crunch, and saltiness of the snot, characteristics that we favor.
But humans are not alone. The authors of the new article reviewed the scientific literature and found 11 species of primates, including humans, macaques and orangutans, pick their noses and many rely on tools like twigs to complete the task; the aye-aye rounds this number up to 12. Although picking your nose may require fine manipulative skills, eating boogers is more democratic. For example, giraffes eat their nasal mucus directly rotating their tongues around their nostrils, the middle finger is not required.
Kali was born in captivity, the daughter of Endora the aye-aye and Nosferatu the aye-aye, both born in the wild. Aye-ayes are only found in Madagascar, where they are endangered due to habitat loss. No one has observed wild aye-ayes picking their noses, and there is a possibility that captive aye-ayes, like Kali, are displaying unusual behaviors. But the researchers stressed that this nose picking could certainly exist in nature and might even have a function that researchers have yet to understand. They conclude the study with a call for further comparative studies of nose picking and mucus eating between the primate and vertebrate kingdom to shed more light on behavior we might dismiss as gross or disgusting. To those who would say no, no to her finger exploits, Kali answers with a stubborn yes, yes.