Sloth hanging

Image by Kung_Mangkorn/iStock

It’s no secret that sloths are some of nature’s slowest beasts, clocking in at a whopping six feet per minute. That’s so slow, it isn’t even worth expressing in miles per hour (but if you’re curious, it’s about 0.06 mph). Clearly, they have nowhere to be, but why do they move so slowly, and why hasn’t such a sluggish animal been picked off by predators? The more answers you have about sloths, the more questions you might find. Let’s start with why sloths are so slow.

It’s not a race

Sloths get by on a vegetarian diet. They amble along, creeping their way along branches while munching leaves and twigs. Part of the reason they move so slowly is that their food doesn’t provide them with a lot of calories, which means they have less energy available to burn. Unlike other tree-bound herbivores, sloths spend about half of the day asleep. In captivity, these slow-moving leaf-eaters have been known to sleep for 16 to 20 hours a day, which leaves little time for eating. In contrast, koalas eat almost a pound of food per day, which is a lot when you consider that they only weigh about 25 pounds. With a diet consisting solely of plant material and not a lot of it, sloths don’t have any substantial reservoir of calories to pull from.

While other arboreal mammals have relatively quick metabolisms, sloths’ digestive systems are as slow as the animals they serve. At any given time, roughly two-thirds of a healthy sloth’s body weight is made up of food in its digestive tract. If you were a sloth, it would take you until Christmas to digest your Thanksgiving dinner. To support such a lazy lifestyle, sloths’ bodies have had to adapt to a minimal effort, minimal energy way of life. Their body temperatures are below-average at 91 degrees Fahrenheit, and their digestive system features a compartmentalized stomach that slowly moves food through, breaking down the tough cellulose in the plants it eats. As a result of their slow metabolism and low body temperature, sloths can survive on minimal food and water.

Despite all odds

Native to the rain, cloud, and mangrove forests of South and Central America, sloths are not without predators. Being slow-moving isn’t the sloth’s only disadvantage against anything that might want to eat it. Other than keeping out of reach, sloths’ only method of defense is taking a swipe at any predator that corners them in the hope that their long claws will scare the predator away. Unless they descend from the treetops, sloths are fairly well hidden from anything that might want to eat them. Because of their humid environments and slow movements, the fur on sloths’ backs grows a layer of algae that helps camouflage them in their treetop environment. From below, they blend in perfectly with the foliage around them. The canopies above shield them from the eyes of any flying predators hungry for a meal.

Across their habitats, the survival of sloths is also due in part to the lack of predators. Jaguars are their main threat near the ground, though these large cats rarely venture too far off the forest floors. Up higher, sloths are susceptible to large birds like the harpy eagle and snakes. As with many animals, humans also present a threat, both environmentally and through hunting. Poachers have been known to hunt sloths, mostly for their meat. However, sloths unknowingly deter most poachers because, even after being shot, most sloths do not let go of their trees, making them difficult for poachers to retrieve. The greater human detriment to sloths comes from encroachment and habitat loss. The majority of sloth deaths in Costa Rica are from sloths grabbing onto power lines. The pygmy three-toed sloth, however, faces extinction due to habitat loss as humans cut down the mangrove forests in which they make their homes.