They Also Serve
from the book, "Petrified Lightning"

Book: 
Petrified Lightning

They Also Serve

Few species in the animal world can boast of contributing a name, as well as a description, to one of the seven deadly sins. For the three—toed sloth, however, being slow (which is what sloth means) in all its movements and bodily functions is a virtue. Slowness made the sloth a valuable resident in the tree canopy of its Central and South American jungle home.

Mammals that have taken to the trees are usually characterized by agility, quick responses, and manipulative hands, feet, and tails—for example, the flying squirrel, all monkeys, the kinkajou, and even the opossum. The three—toed sloth made a radically different adaptation. With hooklike claws it hangs upside down from the topmost branches of the abundant crecopia tree or any of 90 other species of tree and vines. It gets all the food it needs from the foliage, flowers, and fruit of its tree, and sufficient water is available from moisture on the leaves. High above most predators, 30 to 90 feet from the forest floor, it blends unobtrusively with its environment. Remaining motionless and soundless is its way of attracting no attention.

Every feature of the sloth has evolved to make its life simpler and less demanding. Truly it has perfected slothfulness to both a science and an art. In so doing, the sloth defied many rules of how a body should be assembled. Lighter in weight than most animals its size, the sloth has very little muscle, a small heart, an oversized digestive system, a mere stump of a tail, arms much longer than legs, and a neck with nine vertebrae rather than the seven common to most mammals (including the giraffe). Its long, gray—brown hair parts in the middle of its belly and sweeps toward the back to accommodate its upside—down existence.

These physical adaptations simplify the sedentary, leaf—eating, arboreal lifestyle of the three—toed sloth. As it hangs suspended from a limb, rainwater can run off, and its short tail doesn't dangle conspicuously. Its head can turn 270 degrees (three—fourths of a full circle) to eat leaves to the rear or to observe the world with minimal movement. Weighing about eight pounds, it can crawl farther up or out on a limb than any of its pursuers. It can secure itself by a single set of claws and can climb easily and reach far with its long arms.

If an enemy does spot a sloth, what can happen? Hanging upside down puts it out of the grasp of most predators. Jungle cats have no chance unless they happen upon the sloth on one if its rare trips to the forest floor. Snakes have a hard time getting a grip on a sloth suspended from a branch. A harpy eagle may fly down with claws poised to pounce on the sloth, but the living pendulum's long hair and thick skin make it almost impervious to attack. Most predators have discovered that a firmly anchored sloth simply cannot be removed from its perch. Nor is it worth waiting for a better opportunity; weary jaguars give up when they realize that a sloth can outwait anything.

Living is uncomplicated although monotonous for the sloth. With little to fear and no struggle or competition for nourishment, shelter, or protection, the sloth's senses have become dulled and blunted. For an animal that depends on being mistaken for a bundle of dried leaves, this is an advantage.

Although the sloth's activities differ little awake or asleep (while you have been reading this a sloth has done absolutely nothing), 18 out of 24 hours are spent sleeping soundly. The sleeping sloth hangs by its meat—hook claws with no fear of falling. In fact it must consciously unlock its grip to get loose and, according to legend, will remain hanging in place even after death. The sloth does find a change of position necessary when it has eaten all the leaves within its reach. There is also the sloth's regular trip to the forest floor.

Like the rest of the sloth's life functions, digestion proceeds slowly. But the bacteria in its multichambered stomach work constantly to break down the cellulose of leaves into energy. About every eight days the sloth descends laboriously to the base of the tree to urinate and defecate. Hanging on to the trunk with its forelimbs it digs a shallow hole at the base of the tree with its stubby tail. Here it empties bladder and bowels and covers the waste with dead leaves.

Since the sloth wisely does not share its tree, the trip to the forest floor is its only opportunity for a social life. Of course this is a risky adventure for an animal that can only drag itself on its belly when on the ground. But near a pungent dung heap seems to be the only place that a sloth can easily find another sloth, so it is probably here that a pair of sloths meet. They return to the tree for safety more than solitude, and they mate while, what else, hanging from a branch.

About six months later a single infant is born. Sharp claws clamped solidly to its mother's fur, it views an upright world while hanging on to the belly of its upside—down mother. Compared with adults, the infant is a bundle of activity as it climbs around on its mother, sampling her food and lapping water from her coat. If baby and mother become separated, they both call with a frantic "ai!" until they locate each other. This is the sloth's only sound, and in Brazil "ai" is the sloth's name.

Besides being a common trysting place, the sloth dung heap is a perfect place for many insects to lay eggs. Because the sloth returns to the foot of the tree regularly, hatched insects find adequate living quarters in its hair. Researchers have found several species of moths, beetles, ticks, and other mites living on the fur of the sloth. On a single sloth they found 120 moths and 978 beetles, all waiting for their host's weekly trip to the dung heap so they might lay their eggs.

The sloth provides the insects with their most basic needs; the insects merely provide the sloth with additional camouflage. The sloth's original disguise is provided by individual grooved hairs that are usually infested with algae, which gives the sloth a green hue. It can do no more to become part of its environment.

Several researchers have adopted sloths as house pets and learned much more about their life than can be exhibited by a motionless "wasp nest" or "ball of dead leaves" in a fork of a tree 90 feet from the ground. The fact that a sloth in a tree did not react to a gun fired nearby seemed to indicate quite blunted hearing. But longer, closer observation showed that part of its defense is to avoid reacting to any potential threat.

One naturalist placed a plastic disc on a sloth's head while it was asleep. The next morning, about 10 hours later, the disc was still there. On another occasion he noticed the smell of burning fur and discovered the sloth sitting, half asleep, atop a floor lamp. Its rear was smoking, but it continued to sit over the electric bulb. The slow reaction time of a sloth is not surprising; an animal with so little muscle has little energy to spare. Moreover the sloth rarely attempts actively to defend itself and will just make do with status quo. Most wounds a sloth receives slowly repair themselves.

Other sloth observers have seen them swimming over a mile to cross Gatun Lake in Panama. They are excellent swimmers and make the trip regularly. They are at home in water, enjoy a shower, and can be hung on the clothesline to dry while they bask in the sun.

A wildlife researcher kept several sloths as family pets during a four—year study in Suriname. The family was able to witness mating and the birth and rearing of an infant. They found sloths to be extremely adaptable as long as basic needs were met, such as a high place to perch and acceptable food. Sloths learned to accept alternatives to their favorite leaves: hibiscus blossoms, banana peels, cut—up citrus fruits, peanut butter, rice, and a great variety of greens. Although they rarely paid attention to each other, the animals displayed affection and enjoyed attention from the family.

Zoo experiences for the three—toed sloth have been short. Even with a well—duplicated climate and plenty of tropical leaves, it succumbs because of a dietary deficiency. Study of the minerals missing from their food while in captivity has identified the essential ingredient: minerals found in Cecropia ants, which are, for sloths in their home territory, a nuisance that accompanies every meal.

Considering that the sloth is not exactly an overachiever, how does it justify the niche it occupies in the ecological scheme? Actually, the sloth makes very few demands on its environment. Sloths make their homes in a variety of trees, thereby avoiding excessive pressure on any one species. Moreover, by burying their excreta at the base of trees that provide their food, they return to the soil up to 50 percent of the nutritional value of the leaves they eat.

The sloth neither preys on nor competes with any other animal. Its excrement is an ideal site for insect eggs, and it transports the adult insects in its fur, where they can live conveniently and safely. Sometimes doing nothing is exactly what needs to be done. Truly, the greatest service the sloth can render is to hang in a tree and wait.