With its large eyes, bushy tail, and sensitive ears, the aye-aye might seem like a cute if quirky creature. But now researchers have discovered it has a less endearing trait: it uses its long middle finger to pick its nose — and eat the mucus.
Aye-aye are primates — like humans — but they’re nocturnal, critically endangered, and only come in Madagascar. An object of superstition, they have a number of unusual features, including rodent-like teeth and a thin, elongated finger with a ball joint.
While the animal is known to tap hollow wood with its phenomenal finger to locate maggots and fish them out, researchers have found they have video footage of it being used for another, more mundane purpose: nose picking.
“In doing so, this animal inserts its extra-long, thin, and highly mobile middle finger down the full length of the nasal passages and then licks off the collected nasal mucus,” the authors write in the Journal of Zoology.
dr Anne-Claire Fabre, an assistant professor at the University of Bern who co-authored the research, said she videotaped the behavior in 2015 while observing ja-jas caught at the Duke Lemur Center.
“I was really surprised,” Fabre said, adding that the entire middle finger disappeared into the creature’s nose. “It’s almost 8cm long – it’s really long and I was wondering where that finger was going.”
To dig deeper, the researchers created a 3D model using CT scans of the aye-aye’s head and hand to understand where the middle finger went. The results suggested that the digit extended deep into the head.
“That finger basically ends up in the throat,” Fabre said, adding that while nose picking hasn’t been observed in aye-ayes in the wild, that doesn’t mean it doesn’t happen.
The team said the aye-aye was in good company when it came to nose-picking and revealed the trait has been recorded in at least 11 other primate species, including humans, capuchins, macaques, chimpanzees and orangutans, with some species also tools used to the workplace. The researchers said nose picking is most common in species with fine manipulative abilities.
It’s not clear why fingerhunting or other species have a penchant for nose picking, though researchers noted that this may just be an act of “self-cleaning.” But, they added, the fact that multiple species ate the slime suggested there might be other explanations.
Among them, the team noted, were studies that suggested the matter’s “texture, crunchiness, and saltiness” might be appealing, that eating snot might prevent bacteria from sticking to your teeth, and that the trait could strengthen the immune response. There might be a downside, however, they said: Other research has found that nose picking spreads nasal bacteria.
Fabre added that nose picking is under-researched and more research is needed. “You never know where you might end up studying this type of behavior, and sometimes you discover an application that we didn’t expect,” she said.