Sloths are undeniably cute and, to anyone who has ever struggled to get out of bed in the morning, they seem to be living the ideal lazy life. But what other features do sloths have, aside from a kind of shapeless adorability and a relaxed lifestyle? Do sloths have ears?
Yes, they have ears – but since these are very tiny, they are easily overlooked. The hearing ability of sloths is not very good and neither is their sight – even though they have color vision, which is quite rare in mammals. Sloths mostly rely on their senses of smell and touch.
Aside from their small size, there is another peculiar aspect about the ears of sloths. Usually, the vestibular system found in the inner ear is responsible for the sense of balance. Three semicircular canals inside our inner ears respond to specific movements of our heads: looking up or down, tilting our head to the right or to the left, or moving it from side to side.
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When we move, the fluid inside these canals moves, too. When it touches hair cells in small spaces called ampullae, the information of our position in space is sent to the brain.
As most people know – and as their name makes obvious – sloths move only very slowly. They rarely move faster than 0.31-0.36 miles per hour and spend most of their day hanging motionless in trees. This lack of movement also means that they do not need to have a fine-tuned sense of balance.
Therefore, the system inside their inner ears that assures a sense of balance has largely deteriorated. Interestingly, a study from 2012 shows that there is a significant variation in the inner ear canals of different sloths species, depending on how fast they move. Even though all sloths are, in general, lethargic creatures, some are more lethargic than others.
Two-toed sloths are larger and tend to move faster than three-toed sloths, so it comes as no surprise that they have a larger degree of variability in the shape of their inner ears.
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What Are the Differences Between Two-Toed and Three-Toed Sloths?
You might think this is a trick question and maybe are tempted to say that they are basically the same animal, only differing in their number of toes. On the contrary, though, even though they look quite similar, these two families of sloths are not even that closely related!
There are four species of three-toed sloths. They weigh between 3.5 and 4.5 kilograms and can be about 1.5 feet long. When it comes to moving through the trees they are slower than the two-toed sloths, but in contrast to their two-toed cousins, they are quite good swimmers! Three-toed sloths have a short tail.
The name two-toed sloth is a bit misleading. The two species of this family do indeed only have two fingers on their front limbs, but they have three toes on their back limbs, just like the three-toed sloths. They can be more than 2 feet long and weigh 4 to 8 kilograms. Two-toed sloths do not have a tail and have longer fur than three-toed sloths.
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Why Are Sloths Green?
When looking at pictures of sloths you might be slightly taken aback by the green sheen of their fur – this is not a sight one comes across often in mammals! It is not the sloth itself that is so green, but algae growing on its fur. In fact, sloths carry a whole ecosystem around on their backs!
The coarse texture of a sloth’s fur is ideal for collecting moisture, which in turn makes it a perfect home environment for several organisms. Aside from the algae, there are even species of moths that are only found in the fur of sloths! They lay their eggs in the fur and this is also where their larvae grow up until they are ready to take flight. Beetles, fungi, and bacteria also inhabit this furry ecosystem.
Providing a home to other plants and animals is beneficial for sloths, too. The green color of the algae works as a camouflage that hides them from the eyes of predators. This is extremely useful since the slow sloths with their intensely small muscle mass would neither be able to effectively fight nor take flight.