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The Strange Aye-Aye Lemur: Features, Life, and a Pseudothumb

Linda Crampton is a writer and experienced science teacher with an honors degree in biology. She enjoys writing about science and nature.

A Bizarre and Interesting Primate

The aye-aye is a strange lemur that is often said to have a "bizarre" appearance. The animal has large ears, teeth that never stop growing, long and slender fingers, and coarse and untidy hair. It very long and skinny third finger is especially noticeable and is used for a hunting method known as tap foraging. The animal has the large eyes that are typical of nocturnal creatures.

The aye-aye is native to Madagascar but is found in captivity in various countries. Lemurs are primates like us and therefore have five visible fingers and five toes. Researchers have recently made an interesting discovery in relation to the fingers of the aye-aye. They say that an extra and elongated bone inside each of the animal's hands is movable and acts as a sixth digit. They call this digit a pseudothumb and say that it plays a helpful role in the aye-aye's life.

The aye-aye belongs to the class Mammalia and the order Primates, like humans, apes, and monkeys. It belongs to the suborder Strepsirrhini (which contains lemurs, galagos or bush babies, pottos, and lorises), the superfamily Lemuroidea, and the family Daubentoniidae. The derivation of the name "aye-aye" is uncertain.

Habitat and Distribution

The scientific name of the aye-aye is Daubentonia madagascariensis. It's the only living member in the family Daubentoniidae. The animal is arboreal and mainly solitary in the wild. It lives in the rainforest of eastern Madagascar and in smaller areas in the northern and northwestern part of the country.

Madagascar is an island nation off the southeast coast of South Africa. The nearest South African country is Mozambique. Madagascar contains many organisms that are found nowhere else on Earth in the wild, including the aye-aye. It's a unique place.

Location of Madagascar and distribution of the aye-aye according to the last population assessment

Location of Madagascar and distribution of the aye-aye according to the last population assessment

Physical Features of the Animal

An adult aye-aye is about the size of a house cat. Its average body length (excluding the tail) is around sixteen inches. The animal has a small and pointed face that's covered with short hair and has big eyes. Some of the facial hairs are white. The nose is often pink. The rest of the animal’s body is dark brown or black in colour but is sprinkled with white hairs.

The thick and bushy tail of the animal resembles that of a squirrel, while the ever-growing nature of the teeth resembles that of rodents. The long and thin fingers are the most noticeable feature for many people. Each finger bears a curved claw rather than a nail.

When an aye-aye becomes scared or excited, the white hairs on its body may stand erect, making the animal look larger than its real size. This may be a helpful tactic to scare predators away in the wild. Researchers have noticed that captive animals sometimes perform the behaviour when they're moved to a new enclosure or when a mother is playing with her child.

Unfortunately, the animal's strange features have caused some people to believe that its appearance in their community is an evil omen. It's sometimes thought that in order to prevent bad luck from pervading a village, an aye-aye that has been seen must be killed.

Males have huge home ranges, between 250 to 500 acres (100 and 200 ha), while the home ranges of females are much smaller, usually between 75 to 130 acres (30 and 50 ha).

— Duke Lemur Center

Daily Life of an Aye-Aye

The aye-aye spends most of the night looking for food in the trees, but it may spend some time on the ground. During much of the day, the animal sleeps. It makes a nest of leaves in a fork in tree branches. Nest may be used more than once.

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The aye-aye is a territorial animal. Males have much larger territories than females. The territories of different animals may overlap. Meetings between the animals may or may not be peaceful. Duke University says that in general the only social interactions in the wild occur during courtship and when a female is caring for a nursing youngster. Some observations demonstrate that "in general" doesn't mean always.

Some researchers report that they have seen pairs of wild adults travelling through the forest together as they forage, which suggests that they are not always solitary. In captivity, the Duke University scientists have found that "a male/female pair and their single infant might coexist peacefully for years".


The lemur is omnivorous and feeds mostly on insects and fruit. It has an interesting method of finding the larvae in the wood of trees. It taps the tree with its third finger and then listens for the sound created in the hollow passages that the larvae create as they burrow. If it hears the right sound, the lemur gnaws the area with its teeth (if this is necessary) and then extracts the larvae with its finger. The process is sometimes known as tap foraging and is shown in the video below. The elongated finger is also used to scoop the pulp out of fruit and the yolk out of eggs.

The aye-aye has a large brain in proportion to its skull size in comparison to the situation in other lemurs. It's thought that this may be due to the necessity to analyze sound coming from the animal's tree tapping behaviour.

Reproduction in the Species

Duke University has a colony of aye-ayes and has shared a lot of information about the animals on its website. The information includes facts about their reproduction. These facts may or may not apply to the wild animals.

In captivity, the aye-aye breeds at any time of the year. Gestation lasts for about 170 days. The animal produces just one offspring at a time. The Duke University scientists say that in the wild nursing may end when the baby is as young as seven months. In captivity, it may last for twice as long. The captive animals breed every two to three years.

Aye-ayes have lived for as long as twenty-four years in captivity. Their lifespan may be considerably less in the wild where more dangers may be encountered.

The Pseudothumb of an Aye-Aye

Researchers at North Carolina State University used seven aye-aye bodies in their pseudothumb research—six adults and one juvenile. All of the animals had lived in captivity and all of them died of natural causes. They weren't killed for the research.

The Radial Sesamoid

The pseudothumb develops from a bone called the radial sesamoid. The outer of the two bones running down our arm (the one on the side with the thumb) is called the radius. In some mammals, an extra bone is located where the radius joins the wrist bones. This bone is the radial sesamoid. Aye-ayes have the extra bone. Humans sometimes have it, but its presence is rare in us. If it is present in our body, it's generally a small bone.

The Pseudothumb

The pseudothumb of the aye-aye contains an enlarged radial sesamoid bone that looks like an elongated knob. A dense extension of cartilage extends from its tip. (The structure is shown in an animation in the video below.) Three muscles are attached to the radial sesamoid bone via tendons, which could potentially allow movement in multiple directions.

The scientists believe that the aye-aye uses the pseudothumb as an extra digit. This digit is shorter than the other ones and is located within the hand instead of extending from it as the fingers do, but it's believed to be useful.

The Skin Pad

A fleshy pad covers the structures that make up the pseudothumb and is visible on the aye-aye's palm. The skin on the pad has a distinct "fingerprint", or a distinct dermatoglyph as the pattern of skin ridges is technically called.

The scientists say that the long and spindly fingers of the aye-aye help them to get food, but they aren't very good at gasping branches. The pseudothumb and its skin pad likely provide extra gripping ability. The investigators have discovered that some closely-related lemurs don't have a pseudothumb. So far, it appears to be unique to aye-ayes.

A Surprising Discovery

A pseudothumb has been found in a few other mammals, including giant pandas, but it's never been found in a primate before. It seems that no one else has traced the pathway of muscles and tendons to the aye-aye's radial sesamoid bone. This factor may have prevented people from realizing that it might be used as a digit. As the title of the video above says, the pseudothumb is a "secret" finger.

An aye-aye has other pads on its palm besides the one over the pseudothumb. These pads may also be helpful in gripping objects, though not to the extent of the one covering the pseudothumb.

The muscles associated with the aye‐aye pseudothumb are anatomically positioned to enable abduction, adduction, and opposition of this digit relative to the palm.

— Adam Hartstone-Rose et al, American Journal of Physical Anthropology

Aye-Aye Population Size

The IUCN (the International Union for Conservation of Nature) classifies the aye-aye as an endangered animal and says that its population is decreasing. It also says that the animal's population is severely fragmented. Threats include logging and the consequent habitat loss, hunting, and trapping.

The last population assessment was performed in 2018. The number of scientists studying the animal has significantly increased in recent times. As scientists have searched for the animal and found it, they've discovered that aye-ayes appear to be more numerous than was thought at the time of the previous assessment in 2012. The species is still classified as endangered, though.

The aye-aye is a fascinating animal. I hope researchers learn more about its behaviour, its pseudothumb, and its population size. The suspicion that its numbers are higher than was recently believed could be good news. It's important that we know whether the animal needs additional help in order for the species to survive in the wild, however. Hopefully, scientists will soon discover new details about its life.


  • Aye-aye information from the Duke Lemur Center
  • Some facts about the animal from the Encyclopedia Britannica
  • Aye-aye facts from Science Direct via journal and book excerpts
  • The aye-aye entry on the IUCN Red List
  • Researchers discover the aye-aye's extra finger from North Carolina State University
  • The anatomy of the pseudothumb of Daubentonia madagascariensis from the American Journal of Physical Anthropology

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2019 Linda Crampton


Linda Crampton (author) from British Columbia, Canada on February 11, 2020:

Thank you very much for the comment, Peggy. I hope that aye-aye numbers increase, too.

Peggy Woods from Houston, Texas on February 11, 2020:

You come up with the most interesting and informative articles, Linda. I am familiar with lemurs but have never even heard of an aye-aye before reading this. I hope that their numbers increase so that they can be removed from the endangered list.

Linda Crampton (author) from British Columbia, Canada on December 13, 2019:

Hi, Adrienne. I hope the number of aye-ayes increases, too. It's a shame that they are in trouble. They are interesting creatures, as you say.

Adrienne Farricelli on December 13, 2019:

Such an interesting creature! I have seen them before on some animal books, but wasn't aware of their interesting features. Too bad the aye-aye is listed as an endangered species. I hope they find a way to increase their numbers.

Linda Crampton (author) from British Columbia, Canada on December 10, 2019:

Thank you very much for the comment, Chitrangada. I appreciate your visit.

Chitrangada Sharan from New Delhi, India on December 10, 2019:

Haven’t seen or heard about this unique animal, Aye-Aye.

The information you share is interesting indeed. You are doing a great job, by spreading the information.

Always a pleasure to read your articles.Thanks for the education.

Linda Crampton (author) from British Columbia, Canada on December 09, 2019:

Thank you very much, Nell. I think they're lovely animals, too.

Nell Rose from England on December 09, 2019:

I love this little animal. So many people say they are ugly but I think they are beautiful. Great article, and really interesting.

Linda Crampton (author) from British Columbia, Canada on December 05, 2019:

Thank you, bhattuc.

bhattuc on December 05, 2019:

Very interesting and detailed article on aye-aye. Nice reading.

Linda Crampton (author) from British Columbia, Canada on November 26, 2019:

Thank you very much for the kind comment, Chris. The aye-aye has six digits on its front limbs (if the pseudothumb is counted as a digit). It's fascinating to think about how it evolved.

Chris Mills from Traverse City, MI on November 26, 2019:

Fascinating, Linda. You do a wonderful job with these kinds of articles. Since the aye-aye lemur is a relative of monkeys, apes, and humans, I wonder if their hidden thumb is the same digit that developed into our thumbs through a common ancestor. I agree with you. I hope they are found in greater numbers. Thank you for providing such high-quality information.

Linda Crampton (author) from British Columbia, Canada on November 24, 2019:

Thank you very much for the visit and the comment, Eman.

Eman Abdallah Kamel from Egypt on November 24, 2019:

Thank you, Linda, for sharing all this information about Aye-Aye. It is a very useful and educational article.

Linda Crampton (author) from British Columbia, Canada on November 17, 2019:

Thanks, Glenn. I appreciate your comment very much. I think the animal is worth studying. It has some interesting and curious features.

Glenn Stok from Long Island, NY on November 17, 2019:

I've been hearing more and more of the Aye-Aye lately. And your article aroused my curiosity even more. You did great research and covered information that I didn’t find elsewhere.

Their unique and strange body stands out as an odd variation in evolution, but makes sense for their survival. I find it sad that some people kill them for fear that they might bring bad luck.

I find their social behavior interesting, such as when they forage for food, and during courtship or when a female is nursing their babies.

I learned so much from your article, Linda. Thanks for doing the research to write such a detailed review.

Linda Crampton (author) from British Columbia, Canada on November 13, 2019:

Hi, Linda. It's an unusual animal. I wonder whether it has other surprising features that we haven't discovered yet!

Linda Chechar from Arizona on November 13, 2019:

I love the lemurs! Although I've never heard of the Aye-Aye. They're amazing. I didn't realize the brain was to big within its skull. And that pseudo little finger thumb is extremely unusual.

Linda Crampton (author) from British Columbia, Canada on November 12, 2019:

Thanks for the comment, Heidi. The eyes are interesting, as are many of the other features of the animal. I hope that more aye-ayes exist than is realized.

Heidi Thorne from Chicago Area on November 12, 2019:

Those eyes! I've seen pics of these before and those eyes are just incredible. Sad that they're on the endangered list. :( Thanks for sharing your vast knowledge of the animal world with us, as always!

Linda Crampton (author) from British Columbia, Canada on November 08, 2019:

Hi, Liza. I think the eyes of the aye-aye are one of the animal's impressive features. I appreciate your visit and comment.

Liza from USA on November 08, 2019:

The aye-aye is certainly an unusual animal. The eyes remind me of Galagos or bush babies. I must admit never heard of it before, so, thank you for your article, Linda.

Linda Crampton (author) from British Columbia, Canada on November 06, 2019:

Thank you very much for such a kind comment, Devika!

Devika Primić from Dubrovnik, Croatia on November 06, 2019:

Hi Linda I watched documentaries of the The Strange Aye-Aye Lemur of Madagascar and Its Pseudothumb and you top the information here. Interesting , informative and photos are amazing.

Linda Crampton (author) from British Columbia, Canada on November 05, 2019:

Thank you for the visit and the comment, Iqra. It's interesting that some people think the aye-aye is cute and other people think the opposite. It's certainly a thought-provoking animal!

Iqra from Pakistan on November 05, 2019:

i have never heard about this creature, thou it looks cute ... Thank you for sharing so many details about this animal...

An interesting article....

Linda Crampton (author) from British Columbia, Canada on November 05, 2019:

Hi, Denise. It is a fascinating animal. Its action could be a great way to save a tree, as long as it doesn't hurt the tree it by chewing it.

Blessings to you. I hope you have a good week.

Denise McGill from Fresno CA on November 05, 2019:

What a fascinating little creature. It saves the trees when it eats those grubs. Thanks for the info.



Linda Crampton (author) from British Columbia, Canada on November 05, 2019:

Thanks for the visit, Nithya. There's probably a lot that can still be learned about the lemur. I hope its population is doing okay.

Nithya Venkat from Dubai on November 05, 2019:

An interesting read about the Strange Aye-Aye Lemur of Madagascar. Thank you for sharing so many details about this animal, learned a lot today.

Linda Crampton (author) from British Columbia, Canada on November 05, 2019:

Hi, Manatita. I think it's a strange animal as well, but as you say, it's also interesting and amazing. Nature can be fascinating!

Linda Crampton (author) from British Columbia, Canada on November 05, 2019:

Hi, Flourish. The passion of the researcher was nice to see. Scruffy but super is a good way to describe an aye-aye!

manatita44 from london on November 05, 2019:

What a strange animal! Pretty scary, Linda C. I found it very interesting and amazing at the same time. The videos say a lot!!

FlourishAnyway from USA on November 05, 2019:

What a neat scruffy looking animal with super abilities. I was particularly impressed by the passion of that lemur scientist and the fact that he was inspired as a 14 year old from a volunteer experience. It just proves how the impact that adults can have on young people can be life changing and positive.

Linda Crampton (author) from British Columbia, Canada on November 04, 2019:

Hi, Mary. I think the aye-aye is very interesting, too. I think it's worth exploring the animal's behaviour. It may be hiding some more surprising features.

Mary Norton from Ontario, Canada on November 04, 2019:

This is very informative and on a subject I did not know of. What an interesting specie are these ayes-ayes

Linda Crampton (author) from British Columbia, Canada on November 04, 2019:

Thank you for all your comments, Bill. I always appreciate your visits.

Linda Crampton (author) from British Columbia, Canada on November 04, 2019:

Hi, Jana. "Unique" is a great word to describe the aye-aye! It's an unusual animal. I think it's very interesting.

Linda Crampton (author) from British Columbia, Canada on November 04, 2019:

Thanks for the comment, Pamela. I don't think the aye-aye is well known except in a few locations. I think it's worth studying the animal.

Linda Crampton (author) from British Columbia, Canada on November 04, 2019:

Hi, Louise. It's interesting to hear that you think the aye-aye is cute. I wish everyone had that reaction! Thanks for the visit.

Linda Crampton (author) from British Columbia, Canada on November 04, 2019:

Hi, Bill. It is an interesting creature. I think it has several curious features.

Linda Crampton (author) from British Columbia, Canada on November 04, 2019:

Hi, John. I appreciate your comment. The aye-aye is the most incredible lemur that I've discovered so far. I think its behaviour is very interesting..

Bill Holland from Olympia, WA on November 04, 2019:

Always a fascinating read when you publish, Linda, and this is no exception to that rule. Great info as always!

Jana Louise Smit from South Africa on November 04, 2019:

Love this animal. Such a unique look and biology. Thanks for another interesting article!

Pamela Oglesby from Sunny Florida on November 04, 2019:

I must admit my ignorance as I never heard of an aye-aye before. This is a very good, well-written article and I learned so much. Thanks for writing about an animal that isn't exactly a household name

Louise Powles from Norfolk, England on November 04, 2019:

I've never heard of this little animal before, but I must say, I think it looks really cute!

Bill De Giulio from Massachusetts on November 04, 2019:

Hi Linda. I had never heard of the aye-aye. What an interesting creature, I love its eyes. Amazing that they only exist on the island of Madagascar. Thank you for the education.

John Hansen from Gondwana Land on November 04, 2019:

Lemurs are fascinating creatures, and the aye-aye may be the most incredible of them all. A very interesting article, Linda.

Linda Crampton (author) from British Columbia, Canada on November 03, 2019:

Hi, Nikki. Thanks for the comment. The aye-aye is certainly an unusual animal, but I think it's interesting as well.

Nikki Khan from London on November 03, 2019:

Some great facts about this aye-aye animal, it’s eyes looks quite horrific. Haven’t seen such a lemur before. Thanks for adding up to my knowledge Linda.

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