Why Sloths Move Slowly

Oct. 20 is International Sloth Day. Impress your friends (and ace your next Buzzfeed quiz) with these fun facts about sloths.

There is a reason why sloths are synonymous with being slow. A sloth is believed to move only 40 yards (36.5 meters) per day. Their slowness is attributed to their low metabolic rate and their. Sloths are the adorable embodiment of one of the seven deadly sins, suggesting that when these slow-moving cuties die they go straight to hell, giving a whole new meaning to the term 'slow burn'. Here's why sloths are so slow. View full lesson: spend most of their time eating, resting, or sleeping; in fact, they de.

What is a sloth?

Sloths are the stars of memes and viral videos. They make us laugh, and they make celebrities cry. But these social media darlings have been around far longer than the internet. Millions of years ago, giant ground sloths the size of elephants roamed the planet. Some were nearly 20 feet long from snout to tail, with massive claws for pulling tree branches down to eat.

Today’s sloths are a little less intimidating. They max out at about 2.5 feet and weigh between 9 and 17 pounds (about the size of a small dog). They have coarse, brown fur, long limbs and curved claws for hanging tightly onto tree branches — the adaptation to upside-down tree living. And they’re one of the slowest-moving animals on earth!

There are two living families of sloths: two-toed sloths and three-toed sloths. Truth be told, all sloths have three toes on their back feet. But two-toed sloths only have two toes on their front feet, whereas three-toed sloths (you guessed it) have three. Two-toed sloths are also slightly bigger than their three-toed pals.

So, are sloths marsupials or primates?

Trick question. Sloths are mammals, but they aren’t primates or marsupials – though the groups do share some similarities. Koalas, for example, are marsupials that live in trees, eat leaves and have slow metabolisms. But sloths and koalas developed these traits independently of each other. The two aren’t closely related. Sloths actually belong to the superorder Xenarthra and the order Pilosa, with a family tree that includes anteaters and armadillos.

Where do sloths live?

Sloths are found throughout Central America and northern South America, including parts of Brazil and Peru. They live high in the trees of tropical rainforests, where they spend most of their time curled up or hanging upside down from branches. Sloths will sleep, eat, mate and even give birth upside down!

Why are sloths so slow?

Sloths have leafy, low-calorie diets and very slow metabolisms to match. Their metabolic rate is only about 40-45% of what would be typical for their body weight.

Because of this specialized metabolism, sloths need to be frugal with their energy use. So, they move slowly and tend not to wander far from their small home ranges.

Can sloths swim?

Believe it or not, sloths are strong swimmers. Despite their clunky movement on the ground, sloths are nimble in the water where they use a sort of doggy paddle to move around.

Are sloths endangered?

The smallest sloth, called the pygmy three-toed sloth, is found only on a small island off the coast of Panama where it is critically endangered. Some species, like the maned three-toed sloth are considered vulnerable. Others, like the southern two-toed sloth (also called the Linne’s or Linnaeus’ two-toed sloth) are designated as least concern by the International Union for Conservation of Nature.

Are they dangerous?

You tell us:

In all seriousness, you’re unlikely to cross paths with a sloth in the wild (they rarely leave their treetop hideouts). But if you do, like any wild animal, it’s best to keep your distance.

Sloths typically rely on their camouflage to protect themselves from predators. However, when threatened, they can use their 3- to 4-inch-long claws and teeth to defend themselves. And despite their slow movements, sloths are surprisingly strong.

And there are other reasons not to snuggle up to a sloth. Each strand of a sloth’s coarse fur has grooves that run from top to bottom where two types of blue-green algae grow. The green tint of the algae helps sloths blend in to their leafy surroundings, but it also invites ticks, mites, beetles, moths and other creepy crawlies to the party. This little ecosystem created by the algae is so unique that some species, like the sloth moth, live exclusively on sloth fur!

So, do sloths have predators?

Jaguars and eagles are common predators of sloths.

Do sloths have tails?

They’re not much to look at, but three-toed sloths do have short, stubby tails.

What do sloths eat?

Sloths eat leaves, fruit and some select fresh green shoots (they’re not keen on crunchy twigs). Though mostly herbivorous, they may occasionally snack on a larval insect or other passive, protein-packed snack (like a bird egg). They lap dew drops off of leaves and fruits, and get additional water from their food.

Did you know that a sloth’s teeth grow continuously throughout its life? As sloths chomp on plants, their teeth get worn down, which prevents them from getting too long.

It takes a long time for a sloth to digest its leafy diet. So long, in fact, that a sloth usually only climbs down from its tree about once a week to poop!

How much do sloths sleep?

True to their name, sloths sleep for about 15 hours a day. They’re mostly nocturnal, sleeping during the daytime and waking up at night to eat.

How can I help sloths?

Sloths live in rainforests, where habitat destruction is a serious threat. Supporting the responsible use of resources (like choosing Smithsonian Bird Friendly Coffee) can help protect them from habitat loss.

They’re also impacted by wildlife trafficking. Sloths may be amazing and adorable but, like other exotic animals, they don’t make good pets. Their unique diet, lifestyle and health needs require specialized care. Instead, get your fix by visiting sloths at the Smithsonian’s National Zoo or taking home a sloth plush through the Adopt a Species program.

Conventional wisdom has it that sloths are simple, lazy creatures that do very little other than sleep all day. Even the very name “sloth” in most languages translates as some version of “lazy”. It seems astonishing that such an animal survives in the wild at all.

In 1749, French naturalist Georges Buffon was the first to describe the creature in his encyclopedia of life sciences, saying:

Slowness, habitual pain, and stupidity are the results of this strange and bungled conformation. These sloths are the lowest form of existence. One more defect would have made their lives impossible.

Given such a precedent, it is of little surprise that sloths are subject to such profound speculation and misinterpretation, ranging from the benign – that they sleep all day – to the creative anecdotes I regularly hear, such as: “Sloths are so stupid that they mistake their own arm for a tree branch”.

The truth is that sloths are incredibly slow movers, but for a very simple reason: survival. The fact that slow sloths have been on this planet for almost 64m years shows that they have a winning strategy. But in order to understand exactly what it is that makes them such slow movers, and why this works so well, we have to look at the biology of these unusual animals in more detail.

Three-toed sloths are indeed the slowest-moving mammals on the planet, but exactly how slow is slow? At the world’s only sloth sanctuary in Costa Rica, we have been monitoring the movement and activity patterns of wild sloths using small data loggers combined with tracking devices inside specially built “sloth backpacks”. We’ve found that, contrary to popular belief, sloths don’t actually spend inordinate amounts of time sleeping; they sleep for just eight to ten hours a day in the wild. They do move, but very slowly and always at the same, almost measured, pace.

How Fast Do Sloths Move

Moving slowly unequivocally requires less energy than moving fast, and it is this principal that underlies the sloths’ unusual ecology.

Sloths are not the only creatures in the animal kingdom to adopt a slow pace. Cold-blooded ectotherms such as frogs and snakes, are commonly subject to enforced slow movement when faced with cold temperatures, due to their inability to regulate their own temperature independently of the environment. Just like any chemical reaction, cold muscles are slow muscles so cold reptiles are slow reptiles.

This is in stark contrast to most homeothermic mammals which maintain a stable, high core temperature via a process of adaptive thermogenesis, and are consequently able to move fast and effectively regardless of the ambient conditions. But this athletic ability comes at a cost: high body temperatures mean high metabolic rates, and somehow the energy bill must be paid using food.

So where do sloths fit into this dichotomy? They move slowly at all temperatures and, unsurprisingly, deviate from the typical homeothermic mammalian plan by operating at lower body temperatures than most mammals, while apparently having a reduced ability to thermoregulate. The average temperature of the three-toed sloth is around 32.7℃ (91℉), compared to humans’ 36.5℃/97.8℉.

Much in the manner of ectotherms, sloths depend on behavioural and postural adjustments to control their own heat loss and gain, showing daily core temperature fluctuations of up to 10℃. By perpetually moving slowly and partially departing from full homeothermy, sloths burn very little energy and are able to function with the lowest metabolic rate of any non-hibernating mammal, with estimates ranging from 40–74% of the predicted value relative to the sloth’s body mass.

As a result of all this, sloths don’t need to acquire much energy or to spend time looking for it. Both two and three-fingered sloths have a predominantly folivorous (leaf-based) diet, consuming material with a notably low caloric content. There are plenty of other mammals which specialise on a leaf-based diet, but usually these animals compensate for their low-calorie diet by consuming relatively large quantities of food. Fellow leaf-eating howler monkeys move at a normal pace but consume three times as many leaves per kilogram of body mass as sloths, digesting their foodstuff comparatively quickly.

Therein lies another sloth peculiarity: for the majority of mammals, digestion rate depends on body size, with larger animals generally taking longer to digest their food. Sloths appear to break this rule to an unprecedented extent. The exact rate of digestion remains unclear, but current estimations for the passage of food from ingestion to excretion range from 157 hours to a staggering 50 days (1,200 hours).

Unsurprisingly, the sloth’s four-chambered stomach is constantly full, and so more leaves can only be ingested when digesta leaves the stomach and enters the small intestine. Food intake and, critically, energy expenditure are likely limited by digestion rate and room in the stomach. Indeed, the abdominal contents of a sloth can account for up to 37% of their body mass.

All this points to an extraordinary lifestyle, with sloths living on a metabolic knife edge where minimal energy expenditure is finely balanced with minimal energy intake.

How Slow Do Sloths Move

With their plethora of energy-saving adaptations, sloths physically don’t have the ability to move very fast. And with this, they do not have the capacity to defend themselves or run away from predators, as a monkey might. Instead, their survival is entirely dependent upon camouflage – a factor aided by their symbiotic relationship with algae growing on their fur. Sloths’ main predators – big cats like jaguars, ocelots and birds such as harpy eagles – all primarily detect their prey visually, and it is likely that sloths simply move at a pace that doesn’t get them noticed.

The sloth life is certainly not the “lowest form of existence”, but as strategic as that of any other animal. They are energy-saving mammals taking life at a slow pace to avoid the rush and tumble for food, while subscribing the movement patterns that help them avoid being identified as prey. There must be a lesson somewhere in that for all of us.