23.1c – The Aye-Aye

A superstition in the night. (Photo by Frank Vassen)

In Madagascar, a land of strange creatures, one of the strangest of all comes creeping out after dark. Nearly two feet long from head to tail with another two feet of bushy tail behind it, this creature’s large, red eyes peer out through the leaves of a tree. Soon you see its fingers — long, thin, alien, the things of nightmares. With a tap-tap-tapping of its thinnest, almost skeletal finger on the tree, it comes toward you.

The aye-aye is an oddity. Once thought extinct, it was rediscovered in the 1950s and still roams the forests of eastern Madagascar. We call it a lemur, but in truth we aren’t one hundred percent certain what it really is.

The aye-aye, if it is a lemur, is the world’s largest nocturnal primate. The creepy thin hands it sports are a unique evolutionary adaptation that allows it to reach a food source untouched by other animals on the island — insect larvae living beneath the bark of trees, the same food source used by woodpeckers in other parts of the world.

While the woodpecker bores holes in trees with its beak, the aye-aye taps its incredibly thin middle finger up to eight times per second along the bark as it moves. It is able to hear the echoes of its tapping and determine where there are hollow spaces. The creature then gnaws a hole in the bark with its long teeth and inserts its longest finger into the hole to pull out any grubs or other insects living within.

Its teeth grow constantly throughout its life, exactly like a rodent’s teeth, and this prompted early scientists to classify the aye-aye as a rodent. In addition, it climbs trees in a very similar manner to a squirrel, and has some anatomical similarities to rodents as well. Is it possible that some lone species of rodent somehow crossed to Madagascar and evolved into something so strange?

It is possible, but scientists now believe the aye-aye is a primate. What sort of primate is up for debate, but current general consensus is that it is a unique type of lemur, distantly related to the others, highly evolved and specialized to take advantage of a certain food source that none of the other lemurs can access. But in truth, we’re only making educated guesses. It is the only primate known to use echolocation, and we don’t know for certain how it fits into the classification scheme.

The native people of Madagascar don’t know either, and in fact they are just as creeped out by the long fingers and red eyes as we are. The aye-aye also has a somewhat fearless nature, and has been known to stroll into villages or approach humans in the forest. People are afraid of them.

Looking at this, I’m not entirely sure we can blame them. (Image by Joseph Wolf)

In addition to natural fear, the native people believe the aye-aye is evil, a harbinger of death. It is claimed that if an aye-aye points his thinnest tapping finger at you, it has marked you for death. Some believe that the creatures can break into houses in the night and kill a man by piercing the heart with that same long, thin finger. For these reasons, the aye-aye is traditionally killed on sight by natives.

Combined with deforestation, this means that the creature is considered near-threatened, and a second species of aye-aye is believed to have gone extinct within the past thousand years. And there is nothing inherently evil about them, no more so than any other animal and less perhaps than some. They look rather disturbing compared to other animals we are used to, but they are harmless. They eat insects, and will occasionally steal fruit from villages; the rest is superstition brought on by the strange appearance they have evolved to reach their food.

However, even without the superstition, aye-ayes can damage local crops, and are killed by farmers for this reason. Madagascar is not a wealthy nation, and many of its people are poor. Any threat to local food supplies, whether in the field or through thievery from storage areas at night, prompts unfortunate but understandable reactions.

And if you’re wondering where the name “aye-aye” came from, no one quite knows that either, but it’s not because it was named by affirmative sailors. It might refer to a sound that the animal makes; it might refer to the sound the natives make when they see it and run away; or it might come from “heh-heh”, which in a Malagasy language means, simply and appropriately, “I do not know”.

Aye-aye distribution


23.1b – The Dwarf Lemurs

The littlest lemurs. (Gerp’s mouse lemur photo by Blanchard Randrianambinina)

Though all of the lemurs found on Madagascar are a little on the small side — there is, after all, no evolutionary pressure to grow large when you have no competition and live on an island with limited resources — the dwarf lemur family contains the smallest members, and in fact they are the very smallest primates in the world.

There are 31 different species of dwarf lemurs, though many of them are known rather as mouse lemurs. Even the largest is less than a foot tall, and they have exceptionally soft hair. All of the various dwarf lemurs spend nearly their entire lives in trees, where they are agile and comfortable; on the ground they hop on their hind legs like tiny kangaroos, and become easier targets for predators.

As a nocturnal species, dwarf lemurs are not generally as social as most other primates. They tend to live alone or in pairs, though some of them form big sleeping groups during the day so they can snuggle up together. Some of them store fat in their tails, so if you see a dwarf lemur with a big chubby tail, you know it’s well-fed. During dry times and times of food shortages, many of the dwarf lemurs enter a torpor, in which they sit around and use very little external or internal energy to help them survive until food returns.

One of them, the fat-tailed dwarf lemur, enters a full hibernation during the dry season. It is the only tropical mammal and the only primate known to hibernate (discounting, of course, human teenagers during Christmas break). This is interesting because most animals hibernate because of the cold; but even during the dry winter, Madagascar is still very warm, and the fat-tailed dwarf lemur’s body temperature tends to go up and down depending on the weather outside, even while it’s hibernating.

“If your tail was this fat, you’d be sleepy too.” (Fat-tailed dwarf lemur photo by Petra Lahann)

The mouse lemurs are even smaller than the other types of dwarf lemurs. For a long time we didn’t know a lot about mouse lemurs for the simple reason that we didn’t know how many there were. All of the various mouse lemurs look similar to each other, so for a long time we thought there was only one kind. But in the last 35 years we have determined that even though they look alike, there are actually 19 different species of mouse lemur scattered around Madagascar, and perhaps more that we haven’t found yet. One of them, Gerp’s mouse lemur, was only discovered this very year, in 2012.

The smallest primate in the entire world is Madame Berthe’s mouse lemur. It averages only about three and a half inches long, and weighs only an ounce. It can be found only in one small national park on the western coast of Madagascar, and its interesting name comes from Madame Berthe Rakotosamimanana, a woman from Madagascar who founded the Group d’Etudes et de Recherche des Primates (Group for the Study and Research of Primates). Be thankful they didn’t use her full name for the species.

There are no freely-available photos of this lovely small primate, but if you are so inclined, you should click through to this photo to see a baby Madame Berthe’s mouse lemur, which I think you’ll agree is about the most adorable it is possible for a primate to be.

One of the most interesting things about the mouse lemurs is that they all somehow agree to get along and not bother one another. An extensive study was done on Madame Berthe’s mouse lemur and the gray mouse lemur, which live close to one another. They eat the same things and live in the same type of habitat. The gray mouse lemur is larger, stronger, more adaptable, and better able to survive; if it wanted, it could easily push the smaller mouse lemur out, perhaps to extinction. But it does not. The gray mouse lemur’s territory goes right up to the edge of the territory used by Madame Berthe’s mouse lemur, and there it stops.

Why? We don’t know. There are very few animals in the world that share the same resources and the same habitats without one suffering from the presence of the other. But the mouse lemurs, for whatever reason, are content to live with what they have, in the area they call their own, and not to bother their neighbours. If only some of the larger primates could be so reasonable.

“Hi there, neighbour.” (Brown mouse lemur photo by Frank Vassen)

In fact, some dwarf lemurs and mouse lemurs have territories so small that they can only be found around the region of a single village. They are blips on the map, but they are there, living their tiny lemur lives.

But like many lemurs, they are threatened by deforestation across the island. It is entirely possible, given the miniscule territories of some recently discovered mouse lemurs, that entire species of these diminutive primates have already been destroyed before they were ever discovered.

Dwarf Lemur distribution

23.1a – The Lemur

Wet-nosed in a world of their own. (Mongoose lemur photo by IParjan)

For much of its history the island of Madagascar has been shrouded in mystery. Separated from Africa 160 million years ago and from the northward-bound India 90 million years ago, it has been one of the largest isolated areas for evolution outside of Australia, and like that continent-sized country Madagascar is home to many types of creatures found nowhere else on Earth. We looked earlier at the fossa, the Malagasy carnivore that evolved to look like a cat, but the most distinctive animal found on the island is the lemur.

Lemurs branched off from the rest of the primates sometime shortly after the dinosaurs went extinct. In the period from about 65 millions years ago to 50 million years ago — we aren’t exactly sure when in that time frame — the ancestors of all modern lemurs crossed the 350 mile channel between Africa and Madagascar and started an entire new branch of the primate family tree.

How did they cross the channel, you ask? For a long time this was one of the many mysteries of science, because that’s a lot of ocean to cross and the currents go the wrong direction. But it’s recently been proven that because both Africa and Madagascar were further south when the migration happened, the currents back then were in fact going the other way. Thus it is very likely that the ancestral lemurs lived along the African coast and crossed on rafts of vegetation by accident in multiple incidents over millions of years, swept across the channel by the current. It would have been a 30 day crossing for the creatures, difficult but survivable.

When they arrived, singly and in bunches over millions of years, they found what would prove for a long time to be a primate paradise — an uninhabited, unspoiled, enormous rainforest island, a place of wet seasons and dry seasons, a place with few competitors and few predators. And the lemurs took full advantage.

In their tens of millions of years on the island, lemurs evolved into many different forms to take advantage of all the resources and habitats on the island. Some became very small, as small as 30 grams, while others became very large. The largest lemur ever known was Archaeoindris, a lemur that evolved into a shape and size similar to a gorilla, weighing up to 400 lbs. They evolved into all sorts of behaviors, eating habits, movement types, social groupings — the lemurs formed their own diverse range of species on the isolated island, because they had no competition and were not forced to focus on only a few types of living.

But lemurs did not evolve quite the same as the more modern simians such as the monkeys did. Lemurs share the common primate features discussed in the previous article, but they have smaller brains relative to their body sizes, making them generally less intelligent. Lemurs can be taught to use tools in captivity, but they do not do so in the wild.

Either that, or they’re trolling us. Hey, lemur on the right, I see you laughing back there! (Ring-tailed lemur photo by Chris Gin)

Lemurs also have hands that are poorer at grasping than the hands of more modern primates, and lemur tails are not prehensile. This means that lemurs are not so acrobatic in the trees, but they can still get around just fine, and some are almost as good at it as monkeys. In addition, lemurs have generally poor eyesight.

To make up for these downsides, lemurs evolved powerful noses for more than just sniffing. Their noses are constantly wet and can be used as a touch-based sensory organ that lets them smell scent markings left by other lemurs by touching their nose to the marking. Through this method lemurs communicate information about themselves — their territory, their individuality, their gender, etc — without having to see one another, which comes in handy in the dark. Most lemurs are nocturnal, but some come out in the morning and evening as well.

One other thing that all lemurs have in common is the toilet claw. Besides being an object with a great name, the toilet claw is a longer nail on the second finger that is used for scratching and grooming.

But back to Madagascar, where all the lemurs were forming their lemur kingdom in isolation, with no worries and no competition, free to evolve however they wanted to take advantage of the island’s many resources. They were the ghosts of the forest, emerging in the evening and throughout the night to run wild through the rainforests, and indeed that is how they got their name — the word “lemur” comes from a Roman mythological term for ghosts.

“… Boo.” (Red-bellied lemur photo by Rachel Kramer)

But about 1800 years ago, everything changed. That’s when humans not from Africa but from Borneo in Indonesia discovered the island and native tribes colonized it. They were later followed by people from Africa. Together they are today known as the Malagasy people, and with their coming everything changed for the lemurs.

The Malagasy burned and cleared large sections of the rainforest to make room for pastures and rice paddies. So thoroughly did the Malagasy colonize the island that the lemurs, once found everywhere, were soon relegated to only about ten percent of the island’s area. The larger lemurs, including the enormous Archaeoindris, were killed off — as far as we know 17 different species of lemur went extinct in the 1800 years after human arrival.

And that was without hunting. Though the early human activity greatly damaged the lemurs, the people did not hunt or eat them. Lemurs are the subject of a great number of taboos from the native people, and it is believed to be extremely bad luck to harm a lemur.

European scientists have known about lemurs since the 1700s, but almost everything we know about them comes from research that took place only in the past 30 years. We used to believe there were only 30 or so lemur species, but today we know there are nearly 100 different species. Some of the species look so similar that we can only tell them apart with genetic testing.

These hundred or so species of lemur are split up into five major categories, or families, though as always science has not settled on the exact truth of this classification arrangement. Most species today are endangered or threatened due to human activity, especially logging of the Madagascar rainforest.

In the following series of articles we will look at each of the five major lemur families and learn more about these diminutive, diminished former rulers of the isle of Madagascar.

Lemur distribution

23 – The Book of Primates

Time to monkey around. (Chimpanzee photo by Delphine Bruyere)

The order Primates (pronounced, oddly enough, pry-MAY-teez when you are talking about the order, and PRY-mayts when talking about individual members) is one of the largest, most diversified, and most successful orders in the mammal group. They have been around since the fall of the dinosaurs 65 million years ago, and are the kings and queens of mammalian life in the trees.

But before we begin, there is one thing we should get out of the way — yes, humans are primates. However any person wishes to justify it is, personally, fine by me, whether we evolved from more older primate forms or whether God influenced our evolution or whether God sprang us from the ether fully formed with traits that just happen to fit us perfectly into the primate category. That’s up to you, and as business goes it’s none of mine. But the fact of it is essentially unavoidable. We are primates.

There are some who believe that humans should not be placed on the tree of animal life, that we exist beyond it, but we are not some higher form of life. We emerged from the natural processes of the world like everything else. We are intelligent, we are industrious, and we have conquered the Earth’s many habitats like no animal before us has ever done. We have developed language, science, philosophy, and art. We are an amazing, wonderful species when we are at our best. Being a primate diminishes us not at all. Whether we are God’s chosen children or whether we have simply evolved and developed in such a manner as to rise for the most part above our animal instincts, we are still primates. This is where we fit. These creatures are our distant cousins.

That said, I will not be including an entry specifically about humans. The tale of our evolution, mostly known to us but still containing mysteries, is not meant for this record, nor is the long story of our history from our humble African roots to our establishment of civilization to our modern day intelligent adaptation to all the continents of Earth. I may one day tell that story, but the Book of Beasts is for our wild counterparts, and humans are a rather domesticated lot. Besides, we already get our share of mentions when it comes to our actions toward the animals of the world.

The wild primates used to be divided by their dominant features. They were the prosimians, which had features closer to older, more primitive primates, and the simians, which developed later. But today scientists, who do love to muck about with the order of things, instead classify primates by two different features. They are the curly-nosed primates and the dry-nosed primates. Many scientists still prefer the older grouping, which complicates things. Put it out of your mind, gentle reader, and think of monkeys.

Thinking of lemurs is also acceptable. (Red ruffed lemur photo by Hans Hillwaert)

Primates range from very small (the one-ounce Madame Berthe’s mouse lemur) to very large (the 450-pound eastern lowland gorilla), with all sorts of shapes, details, and behaviors in between, but there are a few things they all have in common.

With the exception of humans, as noted above, primates tend to live in tropical or sub-tropical regions where thick forests flourish. They are for the most part tree specialists, you see, and the more trees are around the happier a primate is.

While many animals and even some mammals have evolved to take advantage of trees, primates have truly taken trees to heart. Grasping hands, color vision, developed brains, the ability to walk on two legs, creative thinking — all of these things that helped humans become what we are today initially developed because they are great for living in trees.

Primates all have flexible shoulder joints that let them move their upper arms in many directions. Think of a dog or a cat — they can’t move their shoulders like we can because they did not evolve to move in trees, where such shoulder joints are highly advantageous.

All primates have five fingers and five toes, and have opposable thumbs used for grasping and manipulating objects. These features allow primates to easily climb and swing from branches, and they helped humans become the crafty, technological wizards we are. All primates also have sensitive toes and fingers to help with climbing and balance in the trees, whereas most other mammals have their toes and fingers protected somehow.

Primates have forward-facing eyes that allow accurate depth perception, critical for jumping through trees and also, coincidentally, for driving cars. This is why we don’t let horses drive the school bus. As a bonus, primates can (almost) all see in color.

All primates also tend to give birth to only one young at a time in most cases. As complex mammals, primates require a lot of attention from their mothers, and take longer to fully develop than most mammals, so it is better to have one offspring at a time. Primates are mostly social creatures as well, and typically have dominance hierarchies where one member of each group, typically the strongest, gets to make and enforce the rules over others. Sound familiar?

Last but certainly not least, all primates have large brains relative to their body sizes. A big brain allows for quick, easy processing of all the sensory information involved with swinging through branches high above the ground. This is why the feature developed, but as a side effect all primates are pretty smart cookies as far as animals go, and humans, of course, became the smartest cookies of all — though we did not develop as a distinct species until long after our ancient ancestors came down out of the trees and decided to give the ground a try. Fortunately for them it turned out that having that big brain, those grasping hands that could make tools, and that social cooperation, all of which developed in the trees, let them succeed on the ground as well.

There are a lot of different primates to cover, hundreds of them, so we will lump them together and be brief where we can. But there is a lot to know about these diverse and clever creatures, so let’s begin.

“About time, good fellow.” (Agile gibbon photo by Julie Langford)

22.2a – The Anteater

A nose for nummies. (Giant anteater photo by Malene Thyssen)

The South American grasslands. Night. Vast wild fields roll away in every direction, scattered with countless tall termite mounds, their walls so thickly-built and cemented together that one might almost mistake them for rocks. And shambling out of the darkness across the fields — a strange and shaggy creature that seems almost to have no head, only a neck that gets longer and narrower until it reaches a blunt point. A giant anteater.

The animal walks on its knuckles, but when it stops before the nearest termite mound it unfurls massive, powerful claws like those of a fearsome predator. And it is a fearsome predator, in its way. With great gouges in the hard walls, the giant anteater rips chunks from the earth and exposes the many tunnels of the busy insects. Protected by its shaggy hair from any bite or sting an insect might offer, the creature reveals that what seemed to be its too-long neck is actually simply its head — a head that is narrower than the neck it sits on. With such a long and narrow snout it can shove its mouth directly into the termite tunnels.

Its tongue, longer than its head and attached to its sternum deep in its chest, flickers in and out almost faster than the eye can see, up to two-and-a-half times per second, shooting down into the termites’ home and through its many tunnels. The tongue is a marvel, not only fabulously long but covered in thousands of tiny hooks and coated with a sticky saliva, which combine to snatch up any termites it encounters. The insects it swallows are pulled alive into the anteater’s stomach where hard plates and any dirt or sand accidentally swallowed help to crush and grind the insects into a digestible and nutritious paste.

The termites are no fools, and within a minute they have begun to organize themselves to attack the giant invader, but the anteater is careful. By the time that minute has passed it has gobbled up as many termites as it can and then stops. There are many termites left, but this particular mound is now potentially dangerous. But there are always more mounds, and the creature will visit as many as 200 different termite nests this night before it has eaten enough to see it through the day, which it will spend sleeping in the shade and lowering its body temperature to require less energy.

The giant anteater is the most recognizable of the anteaters, which are closely related to sloths even though they look almost completely different. There were once many different types of anteaters, but competition from species migrating south from North America in the past three million years has reduced the anteater to a mere four species found in central and South America. The giant anteater is the largest, but is also the only one that lives its entire life on the ground.

Consider the silky anteater. The most distant cousin in the anteater family, it is the size of a mere house cat, if not smaller, and can be found in dense jungles instead of grasslands. The silky anteater lives its entire life in the trees, just like a sloth, and it has a prehensile tail to help it climb around in search of insects. But despite its much different appearance and lifestyle, it still employs the same feeding strategy, using a long tongue to lap up insects for nutrition. It sleeps by rolling itself into a ball in a tree, often in such a way that it looks like a seed pod and will thus be left alone.

The littlest anteater, here refusing to show off its powers of camouflage. (Silky anteater photo by Eveha)

Between these two extremes are the tamanduas, the northern tamandua and the southern tamandua to be precise. They are medium-sized anteaters that also have prehensile tails, but they split their time between the ground and the trees. They eat ants and termites with the best of them, but aren’t picky about where to find them.

Fact: ants taste better when eaten upside-down. (Northern Tamandua photo by Dirk van der Made)

Anteaters are not gentle creatures. They aren’t going to storm your home and break down your walls in search of insects, but if you threaten an anteater it will rear up on its hind legs like a bear and will show you exactly how powerful its enormous claws are. Jaguars and large eagles are typically the only animals tough enough to tackle anteaters. They aren’t very nice with one another either. Anteaters are all solitary creatures, and will fight one another if there is a question of territorial rights. When in a scrum, one anteater might even try to climb on top of the other’s back to get an advantage with those claws. Anteaters mean business.

Bonus fact — anteaters are also known as ant bears, though they aren’t related to bears at all, and the scientific name for the anteater group, Vermilingua, means “worm tongue”.

22.1b – The Ground Sloth

Lazy bones? (Photo by Postdiff)

The ground sloths are all gone — so far as we know, they went extinct in the mainland Americas more than ten thousand years ago, and only survived on islands until four thousand years ago, when the last was lost. Under normal circumstances they would not find a place in this blog, for they are no longer a part of the living animal kingdom. But the ground sloths are too fun to pass up, and they also provide an interesting contrast with our living modern day sloths. Plus, they might not be as entirely extinct as we believe.

The ground sloths were most closely related to the modern day two-toed sloth, but they were nothing alike. While the sloths that survived into the present were small tree-dwelling creatures, the ground sloths were terrestrial behemoths.

Ground sloths evolved in South America with the other sloths, and there were five different types of them, each as evolutionarily distinct as dogs are from bears. Even before North and South America joined forces three million years ago, ground sloths made their way north by swimming from island to island in the ocean between the two. When the two continents joined even more ground sloths followed, and eventually they could be found from the southern tip of South America all the way to Alaska.

There were some small ground sloths, but the ones we know best were enormous. Some of them grew larger than modern day elephants, all while maintaining a slothy shape. They had long claws, likely used for stripping the bark from trees, and they could stand on their hind legs to reach tall branches. The ground sloths tromped across the land in search of food while their lazy tree-dwelling cousins stayed at home and very slowly evolved themselves into motionless perfection.

The coming of humans to the continent began the downfall of the giant sloths. They were too big, too slow, and over thousands of years we killed them all, polishing the last ones off shortly after the end of the last ice age. Some survived on islands for several thousand more years, but the youngest confirmed ground sloth we know about died around 2000 BC on Cuba.

But the European explorers of North America didn’t know that. When skeletons of enormous sloths were unearthed, explorers pushing west into the continent’s interior hoped that they might find living giant sloths. As late as the Lewis and Clark expeditions, Thomas Jefferson asked the explorers to keep an eye out for ground sloths, which he believed might still be out there.

And some of the ground sloths likely did survive longer than any provable theory supposes. Preserved ground sloth hide was found in a cave in Patagonia, a remote and mountainous region in the extreme south of South America, by a rancher in the late 1800s, which was dated to about 5000 years ago. This would place the creature on mainland South America thousands of years after they were supposed to have gone extinct.

Indeed, some believe the creatures may have survived on small islands in the Caribbean until as late as 1550 AD. But could the ground sloth still be alive somewhere?

The answer is probably no. But not definitely no. Large parts of South America remain little explored or studied, and native stories in parts of the Amazon and Patagonia tell of creatures resembling ground sloths that some native groups tell us still survive today in the deepest and most remote corners of the continent. A hunting expedition in Patagonia in 1895 reported a close encounter with a large beast much like a ground sloth, with a hide so thick that their bullets were unable to kill it before it retreated.

If there are any still out there, we haven’t found them. They exist only as cryptids, a class of animals that we cannot prove exist today. While some cryptids are likely the result of over-active imaginations or outright fabrication, occasionally a cryptid proves to be a real animal. The okapi was once believed not to exist, and the remarkable coelacanth fish was thought to have been extinct for millions of years before a living specimen was found off the coast of South Africa in 1938.

In today’s world the survival of a beast such as the ground sloth is highly unlikely — but the mystery remains, and a mystery is always delightful.

22.1a – The Sloth

Getting the hang of it. (Photo by Masteraah)

Ah, the sloth. Has any animal’s name ever been so efficiently descriptive, so elegantly appropriate? It’s all right there, one word, five letters — sloth.

Sloths are curious creatures found in the jungles of central and South America. The word “sloth” existed before the scientific community knew about them, a word that meant slow, lazy, lagabout, mud-for-bones, or any number of terms both real and perhaps imagined by the author that come round to the same concept — just plain doesn’t do much. Like a teenager on summer vacation, the sloth fits this term perfectly, so perfectly that we slapped the word right on it as a name.

These creatures are highly distinctive. They are shaped somewhat like large monkeys with their long arms and flat faces, but they are not in any measurable way related to primates. As you know, they are most closely related to anteaters. It’s only that long arms and a generally monkey-like body shape are best suited for climbing in trees, and that’s what sloths do, so this is what they evolved to look like.

Sloths in fact spend almost their entire lives in trees, because that’s where they are safest from predators. But there are many predators in South America that can also climb trees, from the jaguar to large snakes, so what’s this all about?

The key to life as a sloth is in the name. Sloths are known for moving very, very, extremely, quite rather incredibly very slowly. But it’s not laziness. The slowness of a sloth is in fact its greatest defense against predators.

“Don’t mess with me. I’m warning you, if you do, I will sit here. I will sit here so hard, you won’t even know what didn’t hit you.” (Photo by Stefan Laube)

If that makes no sense to you, you’re just not thinking like a sloth. When you don’t move, you don’t attract attention, and when you don’t attract attention, predators don’t try to eat you.

With this in mind, sloths have taken the fine art of not moving to new levels. They spend about ten hours a day sleeping, and the rest is spent hanging upside-down from branches and either not moving or very, very slowly reaching out for leaves to eat. A sloth will only carefully move around in a tree to find new food, or for a bathroom break. When a sloth needs to do its business, it doesn’t simply squat and let it go off the side of a branch. No, the sloth is a more refined creature. About once a week a sloth will very slowly climb down to the ground and relieve itself, then very slowly climb back up.

In fact, scientists have wondered why they do this, because it’s easier to just go from the tree and let it drop, not to mention safer. We don’t really know for certain. Some think it is how sloths find each other for breeding purposes; others think the sloth is worried that going from the tree will make too much noise and attract a predator; still others think the sloth is trying to nourish the tree by burying its excrement near the trunk, thereby helping its own food supply. Or maybe they’re just really fussy. Who knows?

The best part of all this is that it means not only that the sloth digests its food very slowly, but that it stores its excrement inside its own body until it’s ready to do its business. If you kill a sloth close to its bathroom day, there’s a good chance that up to one-third of its body weight will be feces and urine that it was waiting to get rid of. So have fun with that.

This lifestyle serves the sloth very well. For one thing, when you don’t move much you don’t use energy, which means you need to eat less, which means you need to move less. It’s a very happy cycle. For another, the sloth is perfectly adapted for hanging upside down in trees. It is the only mammal with hair that grows toward the body instead of away from it. Look at your arm — the hairs all grow out toward the hand. Look at a dog’s leg — the hairs grow down toward the feet. Not so for the sloth. Its hairs grow the opposite direction, back toward the body’s core, because that way it will still protect against rain when the sloth is hanging upside-down, which it nearly always is.

In addition, sloths have long, curved claws that are not for digging or fighting — though they will take a swipe at you if you threaten it — but for hanging. The claws allow the sloth to hang without any effort, no use of muscle at all. They just dig the claws in, let themselves relax, and hang. This is so effective that even human poachers don’t bother sloths as much as they otherwise might. If you shoot a sloth while it’s hanging, it will simply keep hanging even when it’s dead, held up by its claws, and the poacher would have to climb up and get it. It’s the ultimate post-death screw-you.

Even a sloth that dies a natural death, say from old age, can sometimes remain hanging. They give birth while hanging upside-down, they eat upside-down, they sleep upside-down. To a sloth, the world looks crazy and backward when they stand up straight.

You might not expect it, but sloths can swim. However with all this talk of how slow they are, you might be wondering, really, how slow are they? A sloth in extreme danger of its life will turn up the volume and dash about at an incredible 13 feet per minute. Yes, per minute. Try moving that slowly across your living room without going insane. But remember, that’s only the speed of a really terrified sloth. Normally they only move half that fast at best, and usually even slower.

Two hours later, it finished this bite. (Photo by Fruitwerks)

There’s even a bit more to a sloth’s defense system than sheer slowness, though. They also have camouflage, and it’s about the grossest camouflage you can think of.

Each sloth is essentially its own slow-moving ecosystem. Their hair is host to a number of bacterial colonies that just love sloths, love them so much that a sloth is the only place they will grow, and each baby sloth gets its own bacterial colony from its mother. The bacteria go nuts and cover the sloth’s hair and skin with patches of colour that help the animal blend in with the branches. In exchange for making it harder to see, the sloth lets the bacteria live on its body forever. The bacteria also tends to attract insects, and so you might also find plenty of happy bugs snuggled up with the sloth. They all get along famously, but for the love of God don’t try to pet one.

There are two basic types of sloths alive today, the two-toed sloths and the three-toed sloths. Despite their similar appearance in all things not toe-related, these two types are not very closely related at all.

All sloths have three toes on the back feet, but the two-toed sloths have only two toes on the front feet. These two types of sloths have been evolutionarily separate for more than 35 million years, which is a very long time for two things to be apart and yet still look so similar. The two-toed sloths are much more closely related to the extinct giant ground sloths than to their three-toed distant cousins.

We don’t even actually know what three-toed sloths are related to, or how they came to be. Their line on the tree of evolution is drawn in the shape of a question mark. But it is believed that the two types of sloth evolved independently from ground-dwelling sloths, and that it is sheer coincidence and convergent evolution that they look and behave so much alike. They even both do the inexplicable bathroom thing.

There is, however, one other major difference between the two types of sloth, and it’s a difference that sets each of them apart from all the other mammals as well. For whatever reason, almost every single mammal has seven neck bones, known as cervical vertebrae. You have seven, I have seven, your cat has seven, your hamster has seven, the elephant that hopefully didn’t just step on your hamster has seven, even the long-necked giraffes and the no-neck whales have seven.

But sloths? Sloths said no, no way, that won’t do, and they said it in opposite directions. The two-toed sloths have six neck bones; the three-toed sloths have nine. Why? No one knows. It’s preposterous and mysterious. They don’t need more or fewer neck bones. They’re both practically the same animal, why did they go different directions in terms of more or fewer? What purpose does it serve? Are they just trolling scientists?

We do actually have some idea how this happened, even if the result serves very little purpose. With nine neck bones the three-toed sloth has a more flexible neck than other creatures, but it doesn’t need it; nor does the two-toed sloth needs its more rigid neck. But it comes down to genes.

It turns out that the reason every other type of mammal has seven neck bones, no matter how big or small its neck gets, is that the gene that controls how many neck bones we have is the same gene that helps determine how our nervous systems and our cells grow. If that gene were to change our number of neck bones, there’s a good chance that it would also give us brain problems and cancer, which would keep us (or any other mammal) from passing its different-number-of-neck-bones gene along to any offspring.

So how did the sloth get away with it? It is useful to consider that one other type of mammal also pulled off this trick, and that’s the manatee. We haven’t looked at them yet, but they are slow animals as well, and have six neck bones. The very slow metabolisms of the manatee and the sloth may actually make them resistant to cancer and DNA damage, which would mean that when evolution gave their neck bones a slip, they survived the change and even though it didn’t necessarily confer any specific advantage or disadvantage, they passed it on to their kids with a shrug. A very slow shrug.

Sloths. So weird.

Sloth distribution.