Why sloths are so slow?

Sloths draw our attention with their cute appearance and for being the slowest mammals in the world. They also have green hair and claws like in a horror movie. Do you dare to find out more?

WHO ARE SLOTHS?

Sloths are animals of arboreal habits (they inhabit the humid forests of Central and South America). This could make us think that they are primates. Actually, they belong to a very different group, the same order where we classify anteaters and tamanduas (Order Pilosa). They are also relatives (although a little more remote) of armadillos. The six species that exist nowadays are classified as two-toed sloths and three-toed sloths, although many extinct species are known (some of them giant).

Three-toed sloth (Bradypus variegatus). Photo: Stefan Laube

They have legs with hook-like claws that allow them to hang perfectly from the branches, but on the ground they crawl awkwardly with the claws of the front legs, which are stronger. The three-toed sloth is also a good swimmer.

Unlike anteaters and tamanduas, they have a rounded face and no front teeth. The back teeth work as a shredder and grow continuously.

They have solitary habits.

Two-toed sloth (Choloepus hoffmanni). Photo: Masteraah

AN ALMOST PERFECT CAMOUFLAGE

Sloths have a thick and rough fur, with colors ranging from grayish brown to dark brown, black and even whitish. These colors, added to the slowness of their movements, allows them to go unnoticed. In case of danger, they stay still and if they are discovered by their predators, they will punch with the big claws.

In spite of everything, the fur of sloths can have a greenish color, due to the algae that grows between the hairs. The outer fur is also home to animals such as ticks, mites, beetles and even moths.

green sloth, peresós verd
Sloth with its green fur due to the algae that grow in it. Photo: unknowkn

REPRODUCTION

After mating, the gestation of sloths lasts 5-6 months. A single baby will be born, which hangs from the belly of its mother thanks to its well-formed claws. It will nurse for a month, after this time he will remain attached to the mother to learn the feeding patterns.

 

Mother sloth and baby. Photo: John Martin

FEEDING

Unlike their relatives, who mainly feed on insects such as ants or termites, sloths are folivores or phyllophags: they feed on leaves and buds of trees (especially from Cecropia). Some species complete their diet with insects and the algae of their fur.

Three-toed sloth (Bradypus variegatus) eating. Photo: Christian Mehlführer

They move very slowly through the trees with their hook-shaped claws as they feed. Living in the trees is also a good strategy to avoid their predators (anacondas, harpy eagles, pumas and jaguars, humans …).

In addition to this slowness, their muscles are small and weak for their body size (they have 30% less muscle mass than other mammals of their size). Its metabolism is also extremely slow compared to other mammals. As a result its body temperature is low (about 30° C). Three-toed sloths have the slowest metabolism of all mammals. Two-toed sloths are in the third place, after the panda.

WHY ARE THEY SO SLOW?

Take a loot at this video to see how slow are sloths:

Sloths are so slow that it would take them five minutes to cross a standard-widthstreet. Because their food is almost exclusively leaves, the energy they get from them is very scarce. Leaves have little energy and besides, it is very difficult to extract this energy. As we all know, the same amount of meat would give more energy. Other herbivorous animals supplement their vegetable diet with nuts or fruit, which give an extra boost of energy, but sloths don’t do this.

To counteract this drawback, sloths have two main adaptations:

  • A very large stomach (one third of their body) with several chambers to extract the maximum energy from leaves. This leads to digestions of five or seven days, even weeks.
  • Minimum use of energy, which it means not moving very much and using little energy to maintain their body temperature. To feed without spending a lot of energy, they live almost permanently in the trees and only go down to the ground once a week, to defecate or change to another tree (if they cannot change by the branches to the next tree). They spend most of their time eating, resting or sleeping.

ECOLOGICAL IMPORTANCE

Sloths are great seed dispersers and they fertilize the soil with their excrements.

As mentioned before, algae and moths, among other living beings, live in the fur of sloths. The symbiotic relationship they establish is fascinating. Sloths only come down from the trees once a week to defecate. At that time, moths deposit their eggs in the sloth’s stool. The moth larvae will feed on the feces. Once adult, moths fly to the sloth’s fur, where they will live and mate. Dead moths will be decomposed by fungi that live in the fur, and will transform them into ammonium, phosphates and nitrates that will help the algae to grow. It is believed that sloths complement their diet with these algae, rich in biolipids and other nutrients.

sloth moth, polilla perezoso, papallona peresós
Symbiotic relationship of sloths, algae, fungi and moths (click to enlarge). Source: see image

Besides, the species of micro and macroorganisms that live in their fur have substances against bacteria, cancer cells and parasites such as Plasmodium, responsible for malaria and Trypanosoma, responsible for Chagas disease.

CONSERVATION STATUS

Of the six known species, according to the IUCN Red List, three-toed sloths Bradypus pygmaeus and Bradypus torquatus are respectively critically endangered and vulnerable. The rest are least concern. As usual, habitat destruction is the main threat that sloths face today. Due to their slowness, they are quickly affected by the destruction of the forests that the urban advance entails or they are run over when trying to cross the roads.

green sloth, perezoso verde, peresós cerd, carretera, road, crossing, cruzando
Sloth crossing a road. Photo: Ian D. Keating

Even though they are completely harmless, some people also attack or kill them thinking they are dangerous.

Unfortunately, its friendly face and docile appearance has led to some people to have them as pets. We will never be tired of saying it: wild animals are not pets. Outside of their habitat their physical, nutritional or psychological needs can not be fulfilled. In addition, their extraction from nature is traumatic (they usually kill the mother to capture the young) and transport and storage occur in unhealthy conditions.

Caged sloth. Photo: unknown.

Protection of its habitat and laws in favor of sloths are priority conservation actions, in addition to the existence of rescue centers for injured or orphaned sloths.

Rescued orphan sloth. Phto: Becca Field

WHAT CAN YOU DO YOU?

Education is the most important cornerstone to start respecting nature. Tell the people around you about the unique characteristics of these animals, explain that they are not dangerous to avoid aggressions towards them and make them understand the suffering that involves having them pets. If you live in an area where there are sloths, call the authorities if you see any sloth in danger, trying to cross the road, for example.

If you want to delve into the topic, you can visit the TED-Ed lesson about sloths, the inspiration of this post.

MIREIA QUEROL ALL YOU NEED IS BIOLOGY

Cover image: Getty

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