Nose-picking primates eat their own snot
The internal anatomy of an aye-aye plucking its nose is depicted. Réné Boistel
Have you ever wondered whether animals other than humans pick their noses and consume their own snot? I was shooting an aye-aye at the Duke Lemur Centre when I noticed this behaviour, which is when I originally thought of this question. As I watched Kali (let’s call her by her name) stick the full length of her incredibly long third finger up her nostril, I was both repulsed and impressed (Figure 1).
What direction did that finger go? Figure 2 is a good place to start if you’re unfamiliar with what an aye-aye’s hand looks like. And certainly, the aye-aye’s hand is indeed unique and highly skilled. About two-thirds of the hand’s length, or more than 40% of the forelimb’s total length, is made up of the lengthy and extremely mobile third and fourth fingers. In this fascinating movie, “True Facts about The Aye Aye,” you can learn more about how aye-ayes use their third finger to find food by tapping on wood. This causes acoustic reverberations that allow them to find tasty grubs dwelling in the wood.
My first reaction was to ask my collaborators Erin Ehmke and Christine Wall, primatologists at the Duke Lemur Center, if they knew about nose picking behaviors in aye ayes and other primates. It is from these discussions that this study started, the team of collaborators growing progressively with complementary skills: Renaud Boistel who studied the 3D anatomy of the head in relation to the finger in order to understand where the finger goes when the aye aye picks its nose; Roberto Portela Miguez who helped me conduct bibliographical research; and Louise Peckre who is a specialist in primate prehensile behavior and helped with the interpretation and discussion on the findings in this paper.
We were first struck by the paucity of literature on the subject! Almost all of the literature consists of either behavioral observations or psychological surveys of humans. In addition, most of the information, papers, and books found online are jokes. Therefore, a first step of sorting the information had to be done in order to keep only the relevant ones. What have we learned from this literature review?
1) Picking your nose is not socially accepted (even though the majority of people do it, yes… you’ll have to admit it! Don’t be ashamed!) and it is a fairly recent cultural phenomenon.
2) Over 10 years ago, a researcher wrote a book chapter on the same topic (Portalatin, 2009) and already noted the lack of studies on the issue and encouraged more comparative research. Since then, almost nothing has been done!
3) Nose picking can distribute nasal bacteria (bad… Wertheim et al., 2006) but can help to maintain oral health (good!!! Frenckel & Ribbeck, 2015)
4) Concerning the incredible anatomy of the aye-aye, when it picks its nose, its finger goes into its mouth (and does not scratch its brain)! It is comparable to a very deep covid self-test after all… except that you eat the… you see what I mean.
TAKE HOME MESSAGE: We don’t know whether picking your nose and eating the nasal mucus is good or bad for you. We do know that several species do it. WHY? No idea… but hopefully further comparative studies reassessing this intriguing behavior will provide new insights into its origin, functional role and evolution.