Tag Archives: aye aye

‘Cursed’ yet adorable aye-aye has a sixth ‘pseudothumb’

Exclusively found in the north-eastern parts of Madagascar, the aye-aye (Daubentonia madagascariensis) is a dark-brown or black primate, distinguished by a bushy squirrel-like tail that is larger than its body, bat-like ears, and an over-sized, slender middle finger. But although the species has been known to science since the mid-1800s, scientists have just now discovered that the aye-aye has a sixth digit — a tiny pseudothumb that likely helps the creature grip branches.

The aye-aye uses its exaggeratedly long middle finger to forage for food, typically insects lying within hollow branches. The primate first uses its keen ears to listen for the activity of unsuspecting grub, after which it uses its rodent-like incisors to gnaw through the bark of the branch to make an opening for its middle finger, which is slender enough to nudge right through the hollow tree branch. The finger has a ball-and-socket joint, similar to a human shoulder, which allows a fantastic degree of motion. At the tip of the finger, the aye-aye has a hooked nail that can snag and drag out prey.

Unfortunately for our adorable-looking aye-aye, humans on the island don’t think of it too fondly. Its bizarre appearance is frightening to the locals, and its eery call doesn’t help too much in this regard. According to ancient Malagasy legends, the aye-aye is considered a symbol of death. The natives believe if an aye-aye ever points its middle finger at you, then death will surely soon befall. For this reason, the poor aye-ayes are often killed on sight by superstitious locals. Due to this persecution, as well as habitat loss, the aye-aye is listed as critically endangered, with experts estimating fewer than 1,000 individuals left in the wild. Perhaps that middle finger is rightfully called for.

The aye-aye’s newly found pseudothumb. Credit: Adam Hartstone-Rose.

New anatomical insights, however, are making things more complicated. According to a new study led by Adam Hartstone-Rose, a biologist at North Carolina State University, the aye-aye actually has six digits, which means there’s no actual middle finger. Take that!

“The aye-aye has the craziest hand of any primate,” says Adam Hartstone-Rose, associate professor of biological sciences at NC State. “Their fingers have evolved to be extremely specialized – so specialized, in fact, that they aren’t much help when it comes to moving through trees. When you watch them move, it looks like a strange lemur walking on spiders.”

The reason why it hasn’t been found thus far has to do with the pseudothumb’s anatomy. The bone itself is very small, whereas the rest of the finger is mainly made of cartilage and muscle, which doesn’t show up on X-rays.

The researchers found the tiny thumb by accident while they were employing dissection digital imaging techniques on six aye-ayes. They noticed that one of the hand tendons split from the base of the thumb, heading towards a wrist bone called the radial sesamoid (humans don’t have it).

“Using these digital techniques allows us to visualize these structures in three dimensions, and to understand the organization of the muscles which provide movement to the digit,” says Dickinson, who built the digital model of the anatomy and is co-first author of the paper.

“The pseudothumb is definitely more than just a nub,” Hartstone-Rose says. “It has both a bone and cartilaginous extension and three distinct muscles that move it. The pseudothumb can wriggle in space and exert an amount of force equivalent to almost half the aye-aye’s body weight. So it would be quite useful for gripping.”

According to the researchers, the aye-aye’s elongated middle finger gymnastics doesn’t allow for a very good grip on branches. Like the panda, which also has a pseudothumb, the aye-aye likely uses this extra digit to grasp branches. Besides the aye-aye and pandas, moles also have six digits, which they employ to move more dirt.

“Other species, like the panda bear, have developed the same extra digit to aid in gripping because the standard bear paw is too generalized to allow the dexterity necessary for grasping,” Hartstone-Rose says. “And moles and some extinct swimming reptiles have added extra digits to widen the hand for more efficient digging or swimming. In this case, the aye-aye’s hand is so specialized for foraging an extra digit for mobility became necessary.

“Some other primate species have reduced digits to aid in locomotion. The aye-aye is the first primate to dial digits up in the hand rather than dial them down. And it’s amazing that it’s been there the whole time, in this strangest of all primates, but no one has noticed it until now.”

The findings were described in the American Journal of Physical Anthropology.

Study suggests that primates prefer alcohol in their nectar

Image credit David Haring

Image credit David Haring

From the pubs and bars that line the city streets to the fermented nectars, spas and fruits in nature, alcohol is everywhere. Much like humans, primates have adapted alcohol into their diets and – also like humans – evolved the ability to digest it quickly. Now, a new study shows that the strange aye-aye, a prosimian primate that possesses a genetic mutation also seen in humans and African great apes that accelerates alcohol digestion, prefers alcohol beverages.

The aye-aye is a nocturnal lemur originating from Madagascar with an evolutionary lineage that spans back almost 70 million years. They are some of the strangest creatures on the planet, with unique bony fingers that they use to find grubs in dying tree trunks.

“Aye-ayes are essentially primate woodpeckers,” said Nathaniel Dominy, a professor of anthropology and biological sciences at Dartmouth. “So it is puzzling that they can digest alcohol so efficiently.”

During the wet season, however, the proportion of tree nectar in the aye-aye diet increases. If this nectar is fermented, than a boosted alcohol digestion would start to make more evolutionary sense.

The team tested alcohol preference in two aye-ayes using a nectar-simulation solution of sucrose, as well as the preference of one slow loris, which is the only primate currently known to consume fermented nectar in the wild.

The alcohol concentrations in the nectar-simulation solutions were low, ranging from none to five percent in order to reflect the levels typically found in nature. For each liquid treatment there were two controls of tap water, each placed in a circular array of small-recessed containers in a round resin outdoor table. Positioning was randomized and the experimenters were blind to the contents of the containers during behavioral data collection to eliminate any kind of observational bias.

Each of the two aye-ayes conducted the trial once a day for a total of 15 days and 30 trials between the two of them. Conversely, the slow loris participated in one trial per day over five days for a total of five trials.

The results revealed that the aye-ayes could not only discriminate between the tap water containers and those with alcohol, they adjusted their intake according to the varying alcohol concentrations in the liquid treatments. In addition, they preferred the treatments with the highest concentrations of alcohol and continued to search the high concentration containers long after they were empty.

Data from the slow loris trials was too limited for any statistical results, but discrimination and preference patterns were almost identical.

The results highlight the idea that fermented foods were an important part of our ancestors’ diets and suggest that the genetic mutation that increases alcohol digestion seen in humans, African great apes and aye-ayes is linked to the consumption of fermented fruits on the forest floor.

“This project has definitely fueled my interest in human evolution,” said Samuel Gochman, a student from Dartmouth University and lead author of the study. “Our results support the idea that fermented foods were important in the diets of our ancestors.”

Journal Reference: Alcohol discrimination and preferences in two species of nectar-feeding primate. 20 July 2016. 10.1098/rsos.160217

aye aye madagascar

Meet the aye-aye: the strangest looking primate in the world

aye aye madagascar

Exclusively found in the north-eastern parts of Madagascar, these peculiarly looking primates may both be the strangest and adorable looking things you’ll see all day.


Aye-ayes (Daubentonia madagascariensis) are dark brown or black and are distinguished by a bushy tail that is larger than their body. They also look a lot like gremlins. Distinguishing features include big, penetrating eyes, large sensitive ears and very long and slender fingers. Actually, an aye-aye’s middle finger is particularly longer than the other digits, which the primate makes good use of by tapping trees for wood-boring insect larvae moving under the bark. It employs the same middle finger to fish them out. Yum!

[ALSO SEE] Pica – the practice of eating dirt and soil in Madagascar


I personally find the aye-ayes incredible animals, but the natives have a different story to tell. Because of their bizarre appearance, ancient legends of Malagasy considered it the symbol of death – its eerie call doesn’t help it much either. In fact, that middle finger the aye-aye is so keen on using all the time is what sealed its fate as a death bringer. Natives believe that if an aye-aye points its middle finger at you, then death will soon befall. So… aye-ayes usually get killed on sight. It’s no wonder the species is listed as critically endangered with fewer than 1000 specimens left in the wild.