Sloths grow algae in their fur, and moths live there too.
A sloth moves so little that its shaggy coat becomes a tiny ecosystem. Green algae grow in its hair, camouflaging it in the canopy, and moths live in the fur. About once a week the sloth climbs down, at real risk, to relieve itself, and scientists still argue about why.
Living tree sloths, found in the rainforests of Central and South America, come in two groups: two-toed and three-toed. Despite the names, all have three toes on their hind feet; the difference is in the front limbs. Remarkably, the two groups are only distantly related and evolved their upside-down lifestyle separately, one of the most striking examples of convergent evolution among mammals. Their extinct relatives include ground sloths as big as elephants.
Everything about a sloth saves energy. Its resting metabolic rate is about half that expected for its size, its body temperature drifts with its surroundings, and it spends around 90 per cent of its time motionless, usually moving about 4 metres a minute. Leaves offer little energy, so it has a large, many-chambered stomach in which bacteria slowly break them down; digestion can take a month or more. Even its fur grows the opposite way to most mammals', away from the hands and feet, to shed rain while it hangs. Slowness also helps it escape the notice of hawks and cats that hunt by sight.
The fur hosts green algae that help camouflage the sloth and may supply nutrients, along with a community of beetles, mites and moths. Three-toed sloths descend roughly once a week to defecate at the base of a tree, a dangerous trip for an animal almost helpless on the ground. One explanation involves the moths: they lay eggs in the dung, their larvae feed on it, and the adults fly up to the sloth, where they help fertilise the algae it eats. Another view is that sloths simply inherited the habit from ground-dwelling ancestors and have never been under enough pressure to lose it.
Sloths are also strong swimmers and can slow their heart rate enough to hold their breath for up to 40 minutes. On Panama's Barro Colorado Island they have been estimated to make up 70 per cent of the biomass of tree-dwelling mammals. Two species are threatened: the maned sloth of Brazil's shrinking Atlantic Forest, and the pygmy three-toed sloth, found only on one small Panamanian island.
Source: Wikipedia — Sloth · Text summarised from Wikipedia (CC BY-SA 4.0)
