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What is the laziest animal of all?
If idleness can be judged by the speed at which an animal moves, then the world idleness champion is the sloth. Never was an animal so aptly named.
It looks like a bear about three feet high and usually lives hanging face upwards in a tree.
It is very hard to find a sloth in its hiding-place in the rich foliage of the Amazonian jungles. Its shaggy fur is full of microscopic algae which make it greenish in colour and so provide remarkable camouflage. These algae attract hosts of small insects that feed off them and so find food and shelter in its fleece. Caterpillars crawl between the hairs and spin their cocoons in them. Butterflies hatch out without the sloth being in the least bothered.
Feeding on buds and tender leaves is a tiring occupation since he has to move from time to time. On the ground he has a maximum speed of 150 yards an hour. In the trees, where it moves along by using the long hooked claws at the ends of his fingers, it can reach a speed of half a mile an hour. But it cannot keep this speed up for long. Rapidly exhausted, it stays without moving for hours on end, for days even, and finally takes more than a week to cover the half-mile.
The sloth gives birth to only one off-spring at a time. For a long time the baby lives on its mother's stomach, very near the teats. It even relieves itself there, but this does not disturb the mother who cannot even be bothered to clean herself.
Why is the sloth so slow?
The sloth's method of movement is not a recent innovation since its fur grows in the opposite direction from that of other mammals: from its belly towards its back.
Nevertheless, its great prehistoric cousin, the megatherium walked on the ground. It was bigger than an elephant and had long claws with which it could reach leaves. Then one day in the distant past some sloths perhaps opted to live near the leaves and developed their curious form of locomotion from the habit of reaching out for leaves. As in the case of bats, who hibernate head downwards hanging by their hind legs, the sloth's limbs have muscles which will hold the claws tight round the branch for as long as the animal wishes to hang. They are very unlike ours, which would tend to let go with the effort of hanging for so long. Scientists have found that even the impulses from the brain to the muscles travel more slowly than in other animals.
It is idle and curious on more than one score, and zoologists have put it in the same category as the armadillo: that of the Edentata.