A sloth's body consists of a short neck with four long limbs of equal length, ending in two 3 to 4 inch (8 to 10 centimeter) long curved claws. The head is short and flat, with a snub nose, rudimentary ears, and large eyes. Sloths are a walking ecosystem. They possess a short, fine undercoat, and an overcoat of longer, coarser hairs, which turn green in moist conditions due to algae growth. Each strand of brownish-gray hair has grooves running from top to bottom, where two species of blue-green algae grow. This greenish tint camouflages them in the forest canopy. Their fur also harbors moths, ticks and beetles. Their hair curves from stomach toward their back; this is opposite from most mammals.
Sloths maintain a low, but variable body temperature that ranges from 86 to 93 degrees Fahrenheit (30 to 34 C), which falls during cooler hours of the night, in wet weather, and whenever the animals are inactive. This helps them conserve energy. Sloths have a metabolic rate that is only 40 to 45 percent of what would be expected for their body weight. They have reduced muscles, about half the relative weight of most terrestrial mammals, so they cannot afford to keep warm by shivering. They also regulate their body temperatures by moving in and out of the sun.
Ranging in length from 21 to 29 inches (53 to 74 centimeters) and weighing 9 to 17 pounds (4 to 8 kilograms), this sloth is roughly the size and shape of a small dog.
Two-toed sloths range throughout Central America and northern South America, including portions of Brazil and Peru. Sloths are strictly arboreal, staying high in the canopy of the tropical rain forests and maintaining a range of about 10 acres.
Sloths are usually docile, relying on their camouflage to protect them from predators. However when threatened, they can use their claws and teeth to defend themselves. Mostly silent, two-toed sloths can make hisses or low moaning cries if they are distressed. Sloths have been reported to survive dramatic injuries. Wounds, even deep bites, rarely become infected and seem to heal entirely in less than a month.
Sloths' teeth grow continuously, and have to be worn down by plant material to keep them from getting too long. To compensate for a lack of sharp teeth, they have hardened lips that shear and crop leaves. Southern two-toed sloths eat primarily vegetation, including berries, leaves, small twigs and fruits. They may sometimes eat insects and other small animals. They get water from their food and by lapping dew off leaves and fruits. Food remains in their relatively short digestive tract for approximately one month. They have a low metabolic rate and feces and urine are only passed once a week at habitual sites at the base of trees. At the Zoo, sloths eat a high vegetable diet including kale, corn, apples, leaf eater biscuits, bananas, sweet potatoes and carrots.
Females are sexually mature when they are 3 years old. After that, they breed once each year. Males mature between 4 and 5 years old. After a gestation period of six months, they give birth small, well developed babies; 10 inches (25 centimeters) long and weighing 12 ounces (340 grams). Babies cling to their mother's belly for five weeks, until they are strong enough to move on their own. Mothers spend a lot of time and energy feeding and caring for them, both before and after the young are weaned.
Sloths are primarily nocturnal, sleeping for 15 hours during the day and waking up at night to eat. Sloths move slowly and deliberately. They spend most of their life hanging upside-down from tree branches, whether sleeping, eating, mating or giving birth. They descend to the ground only to change trees and locate new food sources, or to defecate. Because of specializing and slowing their metabolisms, sloths use energy frugally and generally move slowly over small home ranges. Two-toed sloths are well camouflaged in tree canopies. Their most common resting position is to remain curled into a ball in the branches of a tree. In this position, they resemble either a termite nest or a knot in the wood. This, combined with the green color of their fur, makes for great protection from predators.
The average life span of two-toed sloths is 20 years in the wild but may reach over 30 years in human care. The last two-toed sloth living in Amazonia at the Smithsonian's National Zoo was approximately 49 years old when she died, making her the oldest living sloth on record.
Current data shows that sloth populations are stable, but two-toed sloths are a valuable food source and are often hunted for their meat. Two-toed sloths are in serious danger of losing their habitat due to logging of rainforests. Aside from captive animals, rainforests are the only area in the world in which this species lives. Several organizations are currently working to protect these areas. Two-toed sloths also face threats due to trafficking.