The sloth is an animal that uses its claws to hang from branches.
Credit: © Michael Fogden, Bruce Coleman, Inc.

Slow down and wait a minute! Today is International Sloth Day, a day to slow our speed and appreciate the world’s slowest mammal. While many species evolve to eat more, sloths have done the opposite! They evolved in a way that allows them to eat less and survive just by slowing down.

A sloth is a mammal that has a slow and peculiar way of moving. Sloths spend nearly all of their time in rain forest trees in Central and South America, where they travel upside down, hanging from branches with their hooklike claws. Hanging upside down requires almost no energy for a sloth. They can fall asleep in this position and may even stay suspended in the trees for some time after they die. There are two main groups of sloths. One is two-toed and the other is three-toed.

All sloths have small heads, and their noses are blunt. They have peglike teeth. Two-toed sloths also have large sharp teeth at the front of the mouth. Both measure 15 to 30 inches (38 to 76 centimeters) long and weigh 5 to 23 pounds (2.3 to 10.5 kilograms). Their long, coarse fur grows in the opposite direction as that of other mammals, from the stomach towards the back. This allows rain water to easily drain off the body as the sloth hangs. The fur ranges from grayish to brownish in color, which makes them hard to see among the branches.

Sloths turn green in the rainy season from algae that grows in their fur. This helps the sloth blend into the rain forest and protects it from large birds of prey, such as the harpy eagle, and big cats. Sloth fur also provides a home to a variety of invertebrates (animals without backbones) — some of which are found nowhere else on earth. A single sloth can host more than 100 moths and other insects within its fur.

Sloths get little energy from their diet, feeding mostly on leaves. Two-toed sloths may also eat fruits and flowers. They need relatively little food and have a lower rate of metabolism than do other mammals of similar size. Metabolism is the process by which living things turn food into energy. In order to save energy, sloths do not regulate their body temperature like other mammals. They have a lower body temperature than most mammals, which varies with the environmental conditions.

A sloth can take up to 30 days to digest a single leaf. As a result, they have a constantly full stomach. Sloths climb down to the forest floor to defecate (eliminate wastes) about once a week. They can lose up to a third of their body weight in one sitting. Sloths are surprisingly good swimmers. During the rainy season they can swim about three times faster than they can move on the ground.

Although commonly grouped together, the two types of sloths are actually very different animals with very different lifestyles. Two-toed sloths are slightly larger, more active, have a broader diet, and are generally faster-moving than the three-toed sloth. They have brown hair with a long, pinkish, piglike snout. Three-toed sloths have gray hair, a white face and a dark mask around the eyes. Two-toed sloths are primarily active at night, while three-toed sloths are active throughout the day and night. Although almost all mammals possess seven cervical (neck) vertebrae as standard, sloths are one of the few mammals that do not. Two-toed sloths retain only five to seven cervical vertebrae, while three-toed sloths have eight or nine. This unusual trait enables three-toed sloths to turn their head through 270 degrees. This allows them to look for predators and to see the world right side up, while hanging upside down. Sloths can live up to about 30 years.

August 4, 2016

Maps in The World Book Encyclopedia tend to show bodies of water in blue, and, despite the many colors of water we see every day—blue, brown, gray, green, white, clear, or even iridescent—we generally accept that blue represents water. Along the south coast of Western Australia, however, two naturally pink lakes challenge that color representation. The pink lakes lie on the rugged coast near Esperance and on nearby Middle Island in the Recherche Archipelago. The traditionally blue waters of the Great Australian Bight (a large bay in the southeastern Indian Ocean) contrast strongly against the vivid pinks of the lakes. (more…)

March 28

The U.S. Environmental Protection Agency (EPA) released the results of a study on March 26 that revealed that 55 percent of rivers and streams in the United States were in poor biological condition for aquatic life. Nutrient pollution–phosphorus and nitrogen runoff from cities and farms that enters into rivers and streams–formed the  major problem within the 1.2 million miles (1.9 million kilometers) of U.S. waterways.

Large amounts of nutrients in water lead to problems for many animals that live in water. Unnaturally high levels of nitrogen and phosphorus–which are the major components of fertilizer in agriculture and waste in sewage systems–leads to a process known as eutrophication. The excess nutrients benefit algae and allow them to grow much faster. But, an overgrowth of algae, called algal bloom–decreases the amount of oxygen in the water, which leads to the death of fish and other aquatic life. In addition, some algal blooms create poisons (toxins) that are harmful or even fatal to humans.

Excess nutrients from such sources as fertilizers and untreated sewage upset the balance in aquatic systems. This process is called eutrophication. The algae grow faster than the fish can eat them. As more algae grow, more also die and block light needed by aquatic plants. Bacteria use up much oxygen consuming the excess dead algae. The oxygen level of the water drops, causing many aquatic plants and animals to die and decay, using still more oxygen. (WORLD BOOK illustration by Michael Yurkovic)

According to the EPA, their study indicated that the western United States had the best stream and river quality, with 42 percent in good condition. In the East and the plains, only 17 percent and 16 percent, respectively, of waterways were in good condition.

Additional World Book articles:

• Environmental pollution (2008 back in time)
• Water pollution

A website of interest:

• United States Environmental Protection Agency: Nutrient Pollution

November 26, 2012

Animals often feed on plants, and some plants even feed on animals. But researchers have recently identified the first plants that feed on other plants. The cannibalistic plants are green algae, which scientists classify as Chlamydomonas reinhardtii. Although algae are not true plants, green algae are close relatives that ordinarily make their own food through photosynthesis. In photosynthesis, plants and similar organisms use the energy in sunlight to combine water and the gas carbon dioxide, forming sugar. However, the freshwater algae C. reinhardtii often live in the soil, where they may not have access to sunlight and carbon dioxide. Under those conditions, the algae switch to feeding on plant matter in the soil.

The plant matter the algae feed on is cellulose, a tough material in the walls of plant cells and many kinds of algae. Cellulose is a long chain of sugars. The algae release a chemical called an enzyme that can break cellulose apart into simple sugars. The algae then consume these sugars for food.

Microscopic algae often grow in bodies of water. Spherical colonies of the green alga Volvox (above) consist of many cells. Other kinds of algae have only one cell. (E. R. Degginger)

Scientists have identified many plants that live as parasites on other plants. These plants steal nutrients, often by taking the juices of another plant. But the green algae are the first plantlike organisms known to dissolve cellulose, which makes up the body of the plant itself. Previously, only certain bacteria and fungi were thought to have this ability. Researchers suspect that other kinds of algae may also be able to dissolve cellulose.

The discovery may prove useful in efforts to produce biofuels. Biofuels are fuels made from living things that can be regrown quickly. Thus, biofuels are renewable fuels, unlike such fossil fuels as coal and oil. Much research into producing biofuels has focused on growing algae. However, processing the algae into fuel requires using expensive chemicals to dissolve cellulose. An alga that can dissolve cellulose might make biofuel cheaper to produce, helping biofuels to compete with fossil fuels.

The research was led by Olaf Kruse of Bielefeld University in Westphalia, Germany. It was published in the November 20 issue of the journal Nature Communications.

Additional World Book articles:

• Lichen
• The Green Gold of Algal Biofuel (a Special Report)