This Primate’s Long Middle Finger Has a Startling (And Rather Gross) Use

The aye-aye, long seen as spooky, spurred scientists to probe into primate nose-picking

An aye-aye in the grass at night stares at the camera with its right forearm extended.
This aye-aye is not picking its nose, at least at the moment.  Sylvain CORDIER / Gamma-Rapho via Getty Images

Scientists have captured a video of an aye-aye, a kind of primate, picking its nose in a rather gruesome fashion.

The aye-aye is an endangered species that lives in Madagascar, and its closest relatives are lemurs. These small primates are often killed due to their representation in folklore as omens of death, according to IFL Science’s Rachael Funnell.

Their macabre reputation comes in part from a particularly spindly appendage: An aye-aye’s hands make up 41 percent of the length of its forearm. A human with those proportions would have a foot-long hand, per Gizmodo’s Isaac Schultz.

At the end of each of the small primate’s hands are six fingers, including a long and adroit middle finger that can swivel in any direction due to its ball-and-socket joint, like a human shoulder, writes Defector’s Sabrina Imbler.

Aye-ayes use their middle fingers to forage for grubs in trees—tapping on the bark and listening for wood-boring insects moving around beneath it. But, it turns out, the primates can also use the long fingers to forage for something else.

Scientists caught an aye-aye named Kali at the Duke Lemur Center in North Carolina sticking the three-inch-long digit deep into the recesses of its nasal cavity. After extracting the finger, Kali polished it off with a lick.

“It was inserting the entire length and, [when you look at] the length of its head, it was like—where is it going?” Anne-Claire Fabre, a biologist at the University of Bern in Switzerland, tells the BBC’s Maddie Molloy. “I wondered—is it inserting it into its brain? It was so weird and seemed impossible.”

To find the answer, the researchers took a CT scan of an aye-aye specimen from a museum and then modeled the head and hand on a computer, according to Defector. The model showed the finger “going into the sinus and from the sinus into the throat and into the mouth,” Fabre says to the BBC.

Kali’s behavior inspired a deeper search into the world of primate nose-picking. Fabre and her colleagues found examples of 11 other primates in addition to aye-ayes that engage in the habit, including humans, capuchins, macaques, chimpanzees and orangutans, writes the Guardian’s Nicola Davis. The researchers published their findings last week in the Journal of Zoology.

Scientists aren’t sure why primates choose to pick their noses, per the Guardian. “Nearly all the papers that you can find [about it] were written as jokes,” Fabre tells IFL Science in an email.

Many of the studies that do exist are about humans. Previous research has pointed to both pros and cons of eating mucus—for example, one paper from 2015 posits that mucus could protect against cavities. But a 2006 study suggests that nose-picking is associated with Staphylococcus bacteria that can lead to staph infections. In most cases, though, these bacteria cause no symptoms or only mild skin infections.

For aye-ayes, scientists say the snacking habit might have advantages—but without more research, they don’t know if that’s true.

Regardless, co-author Roberto Portela Miguez, a senior curator at the Natural History Museum in London, hopes the new paper will garner more attention for the threatened species, whose continued existence is at risk due to habitat loss and hunting, per CNN’s Charlotte Banks. In fact, aye-ayes were once thought to be extinct, until they reappeared in 1957.

“Aye-ayes are highly endangered and really need our help,” he tells CNN. “Papers like this can hopefully help draw attention to the species, highlight how little we may know about them and get more people to support their conservation.”