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The aye-aye is the newest member of an exclusive club: animals that pick their nose.
The primates from Madagascar have been recorded for the first time inserting their eight-centimetre-long finger almost entirely into their naval cavity, before removing it and licking it clean.
It's something almost all of us have done at some point in our lives, even if we don't want to admit it, but there is no good explanation for why we pick our noses.
Relieving irritation, gaining nutrition and supporting the immune system have been suggested over the years, but as of yet scientists have no firm reason as to why this behaviour should ever have evolved.
The aye-aye, a species of lemur from Madagascar, is the latest to be seen plumbing the depths of their nasal cavity in a new study revealing this behaviour for the first time.
Roberto Portela Miguez is the Senior Curator in Charge of mammals at the Museum and is one of the co-authors sticking their nose into this unusual field of research.
'When I first saw this video, I was really struck by the nose picking,' Roberto says. 'I've never heard of anything like it before outside of humans. It's a surprise because aye-ayes are quite an iconic species, so you would think it would have been reported somewhere before now.'
'We were in for an even bigger surprise when we used CT scanning to see how the nose picking works internally, and the scan was mind-blowing. We were shocked from the reconstruction that the aye-aye's finger could reach through its nose almost to the back of its throat.'
The findings of the study were published in the Journal of Zoology.
Aye-ayes are a species of nocturnal lemur found on the island of Madagascar. They have six 'digits' on each hand, including a pseudo-thumb that helps them to grip and two extremely long fingers that it uses to find and extract grubs from inside trees.
Unfortunately, their forest home is under threat from widespread habitat loss across Madagascar meaning they are classed as Endangered. As a result, many aye-ayes are found in zoos and conservation facilities, including one individual called Kali who lives at the Duke Lemur Center in North Carolina, USA.
It was watching Kali inserting her eight-centimetre-long third finger fully into her nose, and subsequently licking the nasal mucus off of her digits, that inspired this research paper.
Kali's behaviour was recorded by Dr Anne-Claire Fabre, the curator of mammals at the Naturhistorisches Museum der Burgergemeinde Bern and associate professor at the University of Bern. She is the lead author of this new research, and a scientific associate of the Museum.
'I was really surprised to see this,' Anne-Claire says. 'To fit the entirety of its third finger into its nose is pretty impressive! I was trying to imagine where it was going, which helped inspire this paper.'
CT scans revealed that when inserted the finger is long enough to pass through the entire nasal passage, ending up in the pharynx between the back of the mouth and the oesophagus. However, its exact purpose remains unclear.
Comparisons with other species around the world suggest that animals with the ability to finely manipulate objects tended to be nose pickers. Capuchins, for instance, stand out from their close relatives by being able to precisely grip objects by moving their fingers independently.
'We found that the behaviour tended to be reported in species that have a high level of dexterity with their fingers,' Roberto says. 'Non-primates may not possess this same dexterity to pick their nose, and so it may just be a phenomenon that occurs within us and our closely related species.'
Many primates have also been recorded making use of tools, such as twigs, to pick their nose as well, which may extend the potential range of species beyond just those with fingers small enough to fit inside their nostrils.
While some of the animals used in the study are captive, and so could be exhibiting abnormal behaviours, the researchers say that this cannot discount the possibility that nose picking is a widespread behaviour that remains to be properly understood.
'The lack of study so far might relate to it being complicated to investigate, as it's the type of behaviour you might miss if you're not observing an individual all day,' Anne-Claire explains. 'Mammals can be really elusive, which makes this even more difficult to observe.'
'To resolve this, it would be interesting to survey researchers to see if they have observed this behaviour in the wild, and work with scientists in other disciplines to see if nose picking has a functional role or not.'
'It would also be wonderful to help draw attention to the aye-aye, which are highly Endangered. They really need our help, and it would be great to get more people to support them.'
The discovery of nose-picking in the aye-aye now extends the known range of nosepickers into the lemurs, offering further impetus to understand the behaviour.
Nose picking, more formally known as 'rhinotillexis', is the act of extracting mucus from the nasal cavity, while eating it is technically called 'mucophagy'.
Both are often considered socially unacceptable in many of the world's cultures, and it is perhaps because of this that as a behaviour it is relatively understudied. But what research there is, aside from papers written as jokes, suggests the behaviour is very prevalent.
For example, a survey of 254 Americans in the 1990s found that 91% of respondents said they picked their nose, with three quarters professing the belief that 'almost everyone does it.' The behaviour also appears to be independent of other factors such as sex, age and social class.
Meanwhile, the 2001 Ig Nobel Prize for Public Health, an award that 'honours achievements that first make people laugh, and then make them think', was given to two researchers who found that teenagers pick their nose on average four times a day.
While nose picking may not seem like a serious field of study, it can have serious implications. It can become a compulsive behaviour called rhinotillexomania that has even been linked with a death.
Understanding what its purpose is could therefore help make a small but important difference to people's lives. There are some suggestions that it's simply a response to discomfort as mucus dries in the nose, while others suggest it could provide a small amount of hydration.
Some scientists believe that the microbes trapped within it could help maintain the resilience of our immune system. Meanwhile, another study suggests compounds in nasal mucus can reduce the ability of cavity-causing bacteria to attach to teeth, potentially contributing to our oral health.
Before you start brushing your teeth with mucus, however, other research suggests that damage caused by nose picking can help bacteria such as Staphylococcus aureus stick to the inside of the nose, while the act of picking itself can help spread microbes around.
There is also an evolutionary aspect to unpicking rhinotillexis. Nose picking spans the major groups of primates, having been recorded in great apes and both Old and New World monkeys. The apparent reappearance of this behaviour across different groups suggests that it may have some evolutionary function, but the researchers are cautious about this.
'With only 12 species in the study, it's very hard to say if this behaviour is ancestral to primates or has developed independently, or if it even has a role at all,' Anne-Claire says.
'We don't even know if it's limited to primates. We would need a much larger sample to make any conclusions about that, and it would be nice if this paper could kick off research into this topic.'
'Disgusting habits such as coprophagy (eating poo) have a lot of studies devoted to them, so there's no reason why nose picking and snot eating shouldn't be studied as well.'