We recently introduced you to the aye-aye (Daubentonia madagascariensis), a nocturnal lemur who consistently tops the charts as one of the world’s weirdest animals (they even grace the cover of the children’s book Who are you calling weird?). And now, the aye-aye is back with even more weirdness.
One of the traits that makes the aye-aye a weird primate is their excellent wiry-third digit, or their long, thin third finger. Historically, we have known this finger to be a hunting adaptation: the aye-aye moves along branches, tapping and listening. The tapping is meant to spook their prey, and if the aye-aye then hears the rustling of an insect moving within the tree, they then use their (continuously-growing!) incisor teeth to gnaw on the wood and allow their finger an entry point to pierce the larva.
New research published in the Journal of Zoology has discovered another use for this wiry third digit: nose picking. Scientists call this behavior rhinotillexis, and have commonly seen this behavior in humans and other primates who pick their noses and then often inject the nasal mucus. The aye-aye, however, may take nose picking a step further in that they tend to insert their entire finger into the nasal cavity and then lick the nasal mucus from it.
The behavior was first observed on video (see below) by an aye-aye named Kali who lives at the Duke Lemur Center in Durham, North Carolina. The research team, led by Anne-Claire Fabre from the Natural History Museum of Bern in Switzerland, looked to the literature to discover whether other instances of nose picking have been well-documented, finding an instance of capuchin monkeys using sticks to pick their nose and some reports by Jane Goodall in the 1970s. While the behavior is not well-reported, it does seem to be the case that nose picking is more often practiced by primates that have especially good hand dexterity, and/or who use tools (like chimpanzees, gorillas, bonobos, orangutans, and macaques).
Given the length of the aye-aye’s finger, the research team wondered where the finger—which can be up to eight centimeters long—was going. Based on CT scans, the internal nasal anatomy of the aye-aye was studied and the team learned that the finger likely goes down into the throat. Researchers are confident that this was not a one-off behavior; Kali seemed comfortable engaging in it and reports from the staff suggest that they have seen nose-picking before.
Not much is known about why primates like the aye-aye pick their nose, and while one theory is that it could just be for self-cleaning, the fact that they eat the mucus may suggest there is more to the story. One study suggests that the taste and texture could be appealing, though the team behind the aye-aye report posits that it may boost an immune response. For now, though, this study confirms that 12 living primate species pick their noses, and sometimes eat it, and understanding why is yet to be discovered.
Sources: Labroots, Journal of Zoology, Science News 2015, Primates, Science News 2022, Natural History Museum London, The Guardian, CNN