Like all creatures in the animal kingdom, sloths have to excrete metabolic waste in order to keep their bodily functions working properly. In other words, they have to go to the toilet! But of all tree-dwelling mammals, they are the only ones to have developed an odd habit: even if they are high up in the forest canopy, they climb all the way down to the ground to defecate. This strange ritual has scientists baffled. Why would a sloth expend so much energy and make itself vulnerable, while primates simply shift their tails and go from atop their branches? It’s as if we ran five kilometres every time we had to visit the bathroom.
Slothfulness, an evolutionary adaptation
Sloths survive mainly because of their extremely slow and stealthy behaviour. By moving so slowly from branch to branch, they are usually able to avoid the sharp eyes of their main predators, harpy eagles. And so they continue their lazy lives, munching on leaves in the canopy, sleeping and fermenting their meals in their stomachs. Their low-energy diet is enough to keep their slow metabolism going.
Of all the possible hypotheses, the one that has gained the most credence in the scientific community is a lovely story of mutualism, meaning beneficial interaction between one or more species.
In the wild, a sloth’s fur is a veritable ecosystem, home to green algae (Trichophilus spp.) and sloth moths (Cryptoses spp.). When a sloth climbs down to the ground to do its business, all these moths emerge and lay their eggs in its droppings. When the eggs hatch, the larvae then feed on the feces. The cycle is completed the next time the sloth descends, when the larvae – adults by this time – rejoin the colony in the ecosystem in its fur. It is thought that dead moths and moth excrement provide nitrogen, a fertilizer that feeds the green algae. The sugar- and lipid-rich algae is eaten in turn by the sloth. Thanks to its green colour, it also helps our slow-moving friend blend into the background!
A hymn to lethargy
Even though I now understand more about sloth biology and evolution, I am still amazed that in 2015 we share our planet with a creature so different from us. Could Homo sapiens be a bit more “slothful” and spend more time contemplating and less time consuming? If a visitor asks me why it’s so hard to spot a sloth, in the wild or here at the Biodôme, I’ll reply that it’s more than a lifestyle: it’s a survival strategy!