8 Things About Sloths

8 Things About Sloths

Diet

Sloths are mostly arboreal folivores, browsing roughage such as leaves to thrive in trees. Three-toed sloths are strict folivores, whereas two-toed sloths are more omnivorous (should be two/three 'fingered' since there's no difference in their number of foot claws).

Sloths can take up to a month to digest a single leaf because of their extremely low metabolic rate - the slowest of any mammal, despite being warm-blooded. The metabolic rate is less than half of what's expected relative to mass; however, it compensates for their dietary constraints of low energy accrual and nutritionally poor diet, as leaves lack caloric density and can even be toxic - which are ~97% of what they eat.

As digestion takes so long, involving fermentation of leaf cellulose roughage and detoxification, for instance - the stomach is practically always filled and is a massive portion of their whole-body weight. So they can survive on little food each day.

It's speculated that sloths may actually know to sit upright and not hang/move upside down to promote digestive efficiency.

Heterothermy

A method of energy conservation due to sloths' lacking energy acquisition is heterothermy. It involves using a mix of external and self-thermoregulation, implying they have imperfect control over internal temperature - suggesting it fluctuates within much wider limitations in contrast to typical homeotherms like humans (who possess a much more stable internal body temperature regardless of the external environment).

So, a higher sensitivity to change allows them to save energy, as internal processes like thermogenesis (creation of heat) are costly - so they can instead choose to bask in the sun, for example. Still, they are at greater risk of instability than other mammals, which could detriment enzyme and microbe activity for digestion, detoxification and other functional processes.

Locomotion…

As the world's slowest mammal, sloths generally travel an average of ~38 metres a day - making them slower than snails. Again, it's mainly because of their metabolism - although their natural sluggishness correlates with their vital need for energy conservation alongside limiting predator attraction (which is why they're belittled as lazy).

They are so sedentary - also sleeping 15-20 hours a day - that algae (which gives them a greenish hue for camouflage in greenery) and fungi have time to land and grow in their fur, which can protect them from certain strains of bacteria and cancer. They're like a 'moving' ecosystem, e.g. carrying beetles and sloth moths.

Sure, sloths are incredible swingers and climbers, yet terrestrially, their hindlimbs provide no strength, let alone the long claws that make it difficult to walk; therefore, they have to pull with their forelimb claws if there's nothing else to grasp - dragging their stomachs along the ground to move, but only ever when the surface is hard and smooth. If a predator detects one on land, sloths cannot evade, consequently needing to defend via clawing + biting. Even so they're likely finished.

Their otherwise preferred method of travel to find new territory and mates is swimming. Sloths are surprising swimmers, moving up to 3x faster than on land using their lanky arms for leverage as with swinging. They can hold their breaths for ~40 minutes by suppressing their metabolism further to decrease their heart rate by ~66% (where the heart rate is already ~40% that of other mammals).

Defecation?

Defecation is a tremendous exertion for sloths - since only doing so once a week can cause extreme constipation. Furthermore, due to the faecal accumulation, defecation causes a 33% loss of body weight - being more akin to giving birth.

They gradually descend from their tree (rarely coming down otherwise), then eventually perform a 'poo dance' to make a small hole to go into, then covering it after with another dance. In their natural habitat, despite almost always being in a tree, ~50% of all Sloths are predated on outside them - so why do they risk their lives? The process is already draining enough, but they further expose themselves to more predators, where they're even less mobile on grounded. Well...

Sloth Moths

Research has demonstrated that moths living on the sloth's fur get provided the hole the sloth makes to securely lay eggs in the excrement (the larvae are coprophagous) and ensure their lifecycle. Then they go back into the fur to mate - promoting colonisation overall.

Moth colonisation is crucial for the sloths because moths deliver nitrogen by somehow becoming mineralised, due to either or both directly from organic waste products in the stool or from fungal detritivores eating smaller microbes in the fur. The nitrogen abundance increases, fueling algal growth for sloths to supplement their lacklustre nutrition.

Poo -> Moths -> Nitrogen -> Algae -> Nutrients -> e.t.c

So, in a mutually symbiotic relationship (beneficial for both), the sloth fur grants algae shelter, warmth and water as the fur is absorbent. Then, the algae can get eaten - they are easily digestible plus high in carbs + fat for energy reserves.

Anti-predator behaviour

Sloths lack speed as of their metabolism, only moving fast as a last resort - holding 50% less muscle mass than other animals of similar size means utilising too much energy otherwise. They, instead, use their slow lifestyle to avoid detection by vigilant crypsis such as motionless hanging and camouflage to avoid getting predated upon, since a lot of predators' vision and hearing function to detect more mobile prey. Sloths can even sleep by hanging as an inconspicuous ball resembling dead green leaves.

Still, they lack escape options; if they get noticed by their most prominent predator, the harpy eagle, it's probably over. Occasionally, parents will train the fledgling birds using sloths as target practice using their exceptional vision.

Three-toed sloths have two extra vertebrae at the base of the neck, augmenting flexibility to allow a ~270-degree head rotation for predator detection and keeping the nose above water while swimming. On the other hand, their vision gets hindered by rod monochromacy (no cone cells to see in high-light conditions), being colour-blind and not being able to move their eyes. Being practically blind in bright daylight is partway why they're predominantly nocturnal.

Their vision is a factor of why they're slow, having to determine how to manoeuvre around in trees by instead using their adept smell, spatial memory and tactile sensation. Sloths can also adjust their behaviour to seek out shady/dimmer areas in the daytime. Nevertheless, the immense pressure of prevalent nocturnal predators in an ecosystem could shape more diurnal sleeping patterns.

Strength + Grip

Sloths are the genetic pull-up champions. They can do a one-arm pull-up straight out of the womb, even with significantly less muscle than other mammals of similar size. Two-toed sloths are larger, so they may be more powerful concerning propulsion. Arguably more impressively, their hanging ability is unparalleled; even when sleeping or deceased, they can retain their grasp on branches - remaining suspended upright or upside down.

They've evolved structurally for grip, pertaining to swinging, hanging and climbing - to the point of withstanding another animal trying to rip them off. The tendons in the hands and feet help lock them in place to hang for prolonged periods without consuming energy. Furthermore, their claws are long, sharp and hook-like - in addition, they have strong limbs adapted for suspension and stabilisation - such as halting momentum.

The limb muscle fibres are primarily slow-acting for extraordinary fatigue resistance and endurance during constant muscle contraction. But interestingly, they also have elevated anaerobic enzyme activity. For example, 'creatine kinase' for supplying and resynthesising adenosine triphosphate (which muscles consume very slowly), so energy demands are easily met.

When climbing or hanging upside down (~90% of their lives), a sloth's breathing remains unafflicted because the lungs and other organs, like the liver and stomach, are attached adhesively to the lower ribs. Therefore, resisting the extra weight pressure they'd alternatively have to bear - inducing higher energy costs for breathing.

Fighting

Throughout courtship is when a male sloth is least solitary. A female can vocalise a loud mating scream; if more than one male makes an effort to answer, they will fight (the same gender are usually aggressive towards each other anyhow) by hanging on branches and swiping at each other - trying to knock the other off the tree branch.

They can survive falls of ~30 metres without injury; however, the sharp claws lead to brutal scars and possible blinding - even though they have thick skin and withstand severe injuries.

It might appear funny because their facial structure makes them appear as if they're constantly smiling while they rip each other apart. In general, people will subconsciously anthropomorphise them as happy - when really they could be depressed or in pain.