The Web of Life (22-3-16) Sloths & Moths et cetera

 Sloths & Moths et cetera

It’s almost as if people don’t want to know the truth about sloths. There’s something charming about thinking of them as lazy and stupid. ~ English zoologist Becky Cliffe

Sloths come by their name honestly. Besides sleeping 9.5 hours a day, they do a lot of nothing. When a sloth does move, it does so slowly. Top speed in the trees, trying to escape a predator, clocks at 4 meters a minute. On the ground, half that at best.

A sloth spends its life hanging from a tree in a tropical rainforest. Sloths eat and sleep in the trees. They even give birth in a tree. Too lazy to hit the ground upon their demise, some even remain hanging from a branch when dead.

2-toed sloths forage for leaves widely across the treetops, albeit at a leisurely pace. Its 3-toed relative cannot be bothered with that much exertion.

3-toed sloths have 1/4th the muscle tissue of comparably sized mammals; another disincentive to a vigorous life. They have the slowest metabolic rate of any mammal, and a low body temperature even when allegedly active.

Leaves are a poor source of nutrition. Animals that depend upon them, such as gorillas, typically have a large gut to accommodate their digestion. Living in the trees, sloths cannot afford such tummy luxury.

About the only time a sloth is on the ground is to literally lay waste. It digs a hole to urinate and defecate, then covers it up afterwards, to avoid giving away its location. Digestion is so slow that a sloth only needs to go once a week. The 2-toed sloth lets loose from the trees, while the 3-toed sloth climbs down to the ground.

Considering their speed, sloths are at greatest risk when on terra firma. Being caught on the ground is the leading cause of sloth death. Dropping waste from the trees is also a hazard, as it allows predators to more easily locate them, especially considering how little they move. The only time that 3-toed sloths dump from the trees is during a rainstorm, when waste readily washes away.

Despite staying in one place, sloths attract little attention. Sloths’ only predators are Jaguars and harpy eagles. Jaguars can climb trees but can’t reach sloths on the branches that sloths prefer, as these limbs are too slight to support a jaguar’s weight. Harpy eagles, which diet on monkeys and opossums, can see and snag a sloth only if it carelessly exposes itself on an ill-chosen branch.

Everything in the forest can eat them. So they have to be careful to go undetected, and one of the best ways to do that is to be very slow and very quiet. ~ American zoologist Sam Trull

Thanks to their long, curved claws, sloths hang upside-down for hours on end. The constant grip is possible because of a lattice of tendons in the hands and feet that draw their digits closed while at rest. That, and sloths are surprising strong, and their muscles resist fatigue.

Sloth muscles employ unique enzymes that confer tolerance to heavy accumulations of lactic acid, which wear muscle strength down. The sloth’s protein profile (proteome) is like fast-running cats such as cheetahs.

Sprinting is all about anaerobic power for short durations. So it is odd that a sloth that hangs for extended periods of time matches that metabolic profile. ~ American zoologist Michael Butcher

Moths that live within the sloth’s fur plant their eggs in sloth excrement, which their caterpillars consume before becoming adults, whereupon they fly up to become part of the sloth ecosystem.

When a moth dies on a sloth, its body is decomposed by fungi that live there. That releases nitrogen and other nutrients to feed the copious algae that live on the sloth. The strands of a sloth’s fur are grooved to trap rainwater and provide an ideal environment for the algae.

A sloth grooms itself so slowly that the moths within have no trouble escaping before getting raked. Grooming harvests the algae, which provides essential nutrition to the 3-toed sloth.

The algae are highly digestible, and far richer in fat than the leaves which are so slowly chewed. The leaves are a supplement, as a 3-toed sloth expends more energy than it takes in from eating leaves.

The 2-toed sloth has a similar system, but its symbiotic colonies are less fulsome, and so its reliance upon leaves greater. By living in the trees lower down, and taking the trouble to poop on the ground, the 3-toed sloth minimizes its exertions and maximizes its ease, while its colonial friends do as they please.

They are very economical animals and they make the most of every single thing they have available to them. ~ Becky Cliffe

The greatest mystery surrounding sloths is their near invincibility.

Of all animals, this poor, ill-formed creature is most tenacious to life. It exists long after it has received wounds which would have destroyed any other animal. ~ English naturalist Charles Waterton in 1828

Why and how sloths are capable of bouncing back after horrible injuries is still a mystery. ~ Becky Cliffe