When many people see a sloth for the first time, they think that it is either tired or lazy. In fact, the word "slothful" means "lazy." Sloths are not actually weary or lazy, but many people make these false assumptions because sloths sleep so much (up to 15 hours per day!) and because they move at an incredibly slow pace.
Sloths are so sluggish because they are designed to live off of very little food (food is how animals get their energy). Since sloths do not eat many calories (energy stored in food), they have very little energy to carry out their bodily processes like digesting food and regulating body temperature. In other words, sloths have a very slow metabolism (the rate at which their bodies use energy).
There are two types of sloth: the two-toed sloth and the three-toed sloth. These names refer to the number of toes on the animals' forelimbs (arms). However, there are other differences as well. Two-toed sloths have longer legs, do not have tails, and are omnivores (they eat plants and small animals). In contrast, three-toed sloths have shorter legs, are equipped with tails, and are herbivores (they only eat plants). Both types grow to be 1 1/2 to 2 1/2 feet long.
Two-toed and three-toed sloths both evolved from the Giant Ground Sloth, an herbivore that was about the size of an elephant! For reasons that are still unknown, the Giant Ground Sloth became extinct in North America about 10,000 years ago. As a result, the sloths that we see today are native only to Central and South America.
In contrast to the Giant Ground Sloth, modern day sloths rarely go down to the ground. Instead, they spend virtually their entire lives hanging upside down in trees!
This upside down position is the reason that many of their internal organs (e.g. stomach and liver) are located in different places than they are in other mammals. In addition, a sloth's hair curves from its stomach to its back, which is the opposite direction of hair growth on most animals.
Speaking of hair, sloths have excellent camouflage (physical traits which help them to blend into their surroundings in order to hide from predators). Sloth hair is grey and brown so that it matches tree bark.
However, sloths often have a bluish-green appearance during rainy months because the extra moisture in the air allows algae to grow on their fur. Since the rainy season allows more leaves and moss to grow on the trees, having a bluish-green coat helps sloths to blend into their environment.
Little Lion Experiment:
Unlike most mammals, sloths allow their body temperature to fluctuate somewhat along with their environment. So, their bodies get colder at night and during the rainy season.
As a result, their digestion slows during these times. This is because their digestion processes are temperature-dependent. In other words, the warmer a sloth's body is, the faster it will digest food.
So, if sloths get cold enough, then they can not digest food quickly enough to survive. This means that sloths can actually starve in cold weather even if their stomachs are full of food!
To examine temperature-dependence, fill a Styrofoam cup with 2 inches of very cold water. Place a wooden toothpick into the water and leave it there for the rest of this experiment (it will reduce 'bubbling over' in the microwave).
See how much salt you can dissolve into the cold water. Remember, dissolved salt is invisible, so as soon as you see salt at the bottom of the cup, then stop adding salt! Intact salt means that you have dissolved all the salt you can at this temperature.
Microwave the cup for 10 seconds, then wait 15 seconds before opening the microwave door. Next, take the cup out of the microwave, carefully swirl it, then see if you can dissolve more salt into the water. Microwave for 10 seconds more, wait 15 seconds, and see if you can dissolve more salt. Note: do not repeat these steps again or else the water will become dangerously hot!
Do you notice a relationship between the temperature of the water and the amount of salt that can be dissolved in it?