Nose-picking primates are helping scientists to understand the evolution and possible functional role of the behaviour in humans.
For the first time researchers have recorded the aye-aye – a long-fingered lemur – inserting its longest finger up its nostrils and then licking its finger clean.
So far 12 other primate species, including humans, have been documented picking their nose and eating the mucus.
The scientists said their findings, published in the Journal of Zoology, could shed some light on how this behaviour has evolved and whether it has a functional role.
The lead author Anne-Claire Fabre, a scientific associate at the Natural History Museum in London, said: “There is very little evidence about why we, and other animals, pick our nose.
“Nearly all the papers that you can find were written as jokes. Of the serious studies, there are a few in the field of psychology, but for biology there’s hardly anything.
“One study shows that picking your nose can spread bacteria such as staphylococcus, while another shows that people who eat their own snot have fewer dental cavities.”
The aye-aye, the world’s biggest nocturnal primate, belongs to a category of species known as strepsirrhine primates and is native to Madagascar.
It has rodent-like teeth and a specialised long, thin middle finger.
The aye-aye’s fingers are used to locate food inside wood by tapping on it and then extracting small grubs. The researchers also noticed the lemur uses its longest finger to pick its nose.
Ms Fabre said: “It was impossible not to notice this aye-aye picking its nose.
“This was not just a one-off behaviour but something that it was fully engaged in, inserting its extremely long finger a surprisingly long way down its nose and then sampling whatever it dug up by licking its finger clean!”
The researchers used a CT scan to look inside the skull and hand of an aye-aye specimen at the museum and found that the finger could go all the way into the throat.
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Previous scientific research has suggested there may be health benefits to eating snot, but the researchers believe that in this case there is a chance that the animal ingesting its own mucus may simply be down to its texture, crunchiness and saltiness.
Roberto Portela Miguez, a senior curator at the Natural History Museum and a co-author of the paper, said: “It is great to see how museum specimens and digital methods can help us elucidate behaviours that are generally quite difficult to observe in their natural habitat.
“We hope that future studies will build on this work and help us understand why we and our closest relatives insist on picking our noses.”
