The Strange Aye-Aye Lemur of Madagascar and Its Pseudothumb

Updated on November 3, 2019
AliciaC profile image

Linda Crampton is a writer and teacher with an honors degree in biology. She loves to study nature and write about living things.

An aye-aye in a zoo in Madagascar
An aye-aye in a zoo in Madagascar | Source

A Bizarre Animal

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. It contains many organisms that are found nowhere else on Earth in the wild, including the aye-aye.

Distribution of the aye-aye according to the last population assessment
Distribution of the aye-aye according to the last population assessment | Source

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 and mostly white hair. The nose is often pink. The rest of its body is dark brown or black in colour but is sprinkled with lighter hairs. The thick and bushy tail 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.

A wild eye-eye
A wild eye-eye | Source

Daily Life of an Aye-Aye

The aye-aye spends most of the night looking for food in the trees. 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.

Territoriality

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 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".

Diet

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

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. Threats include logging and the consequent habitat loss, hunting, and trapping.

The last population assessment was performed in 2012. The number of scientists studying the animal has significantly increased since that time. 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 last assessment.

The aye-aye is a fascinating animal. I hope more is learned 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. Hopefully a new population assessment will be performed soon.

References

  • 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
  • A bizarre primate with a newly-discovered digit from National Geographic
  • 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

Questions & Answers

    © 2019 Linda Crampton

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      • AliciaC profile imageAUTHOR

        Linda Crampton 

        3 days ago from British Columbia, Canada

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

      • lindacee profile image

        Linda Chechar 

        3 days ago from Arizona

        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.

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        4 days ago from British Columbia, Canada

        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.

      • heidithorne profile image

        Heidi Thorne 

        4 days ago from Chicago Area

        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!

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        8 days ago from British Columbia, Canada

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

      • lizmalay profile image

        Liza 

        8 days ago from UT,USA

        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.

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        10 days ago from British Columbia, Canada

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

      • DDE profile image

        Devika Primić 

        10 days ago from Dubrovnik, Croatia

        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.

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        10 days ago from British Columbia, Canada

        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!

      • Iqra431 profile image

        Iqra 

        10 days ago from Pakistan

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

        An interesting article....

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        11 days ago from British Columbia, Canada

        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.

      • PAINTDRIPS profile image

        Denise McGill 

        11 days ago from Fresno CA

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

        Blessings,

        Denise

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        11 days ago from British Columbia, Canada

        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.

      • Vellur profile image

        Nithya Venkat 

        11 days ago from Dubai

        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.

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        11 days ago from British Columbia, Canada

        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!

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        11 days ago from British Columbia, Canada

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

      • manatita44 profile image

        manatita44 

        11 days ago from london

        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 profile image

        FlourishAnyway 

        11 days ago from USA

        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.

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        12 days ago from British Columbia, Canada

        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.

      • aesta1 profile image

        Mary Norton 

        12 days ago from Ontario, Canada

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

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        12 days ago from British Columbia, Canada

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

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        12 days ago from British Columbia, Canada

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

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        12 days ago from British Columbia, Canada

        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.

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        12 days ago from British Columbia, Canada

        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.

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        12 days ago from British Columbia, Canada

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

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        12 days ago from British Columbia, Canada

        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..

      • billybuc profile image

        Bill Holland 

        12 days ago from Olympia, WA

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

      • Jana Louise Smit profile image

        Jana Louise Smit 

        12 days ago from South Africa

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

      • Pamela99 profile image

        Pamela Oglesby 

        12 days ago from Sunny Florida

        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

      • Coffeequeeen profile image

        Louise Powles 

        12 days ago from Norfolk, England

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

      • bdegiulio profile image

        Bill De Giulio 

        12 days ago from Massachusetts

        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.

      • Jodah profile image

        John Hansen 

        12 days ago from Queensland Australia

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

      • AliciaC profile imageAUTHOR

        Linda Crampton 

        12 days ago from British Columbia, Canada

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

      • nikkikhan10 profile image

        Nikki Khan 

        12 days ago from London

        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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