Photo: Garst, Warren, 1922-2016, photographer · CC BY-SA 4.0
Green fur
Sloths move so slowly that algae grows in their fur, turning them slightly green.
4 min readLast updated
The short answer
Yes. Green algae grow in the fur of sloths, especially three toed sloths, giving them a greenish tinge. Their hair is grooved to hold water, creating a tiny ecosystem.
Why it's true
Sloths spend most of their lives hanging still in rainforest trees, moving only a few meters at a time. Their outer hairs have cracks and grooves that soak up rainwater, providing the perfect home for algae. In the humid rainforest, the algae thrive and can make the sloth look green, which helps it blend in with leaves.
Sloth fur hosts much more than algae. Scientists have found fungi, beetles, mites and specially adapted moths living in it. Some sloth moths spend almost their whole adult lives in the fur. A 2014 study suggested a fascinating cycle: moths lay eggs in sloth dung, the moths help fertilise the algae, and sloths may lick the algae as a nutritious snack.
Their slowness is a smart energy saving strategy for an animal that eats low energy leaves.
By the numbers
6
Living sloth species
~1 week
Between trips to the ground
2014
Fur ecosystem study published
Up to 30 days
To digest a meal
How we know
Researchers studying sloths in Central and South America noticed their green tint and examined the hairs under microscopes. They found algae species that appear to live almost only in sloth fur, suggesting a long relationship between the animals.
The 2014 study, published in Proceedings of the Royal Society B, compared three toed and two toed sloths. Three toed sloths, which climb down to the forest floor to defecate, had more moths and more algae in their fur. The researchers proposed that this risky trip down the tree helps support the moth and algae community, though some parts of the idea are still debated.
A risky bathroom break
Climbing down to the ground once a week exposes sloths to predators and uses precious energy. Scientists have long wondered why they do it.
One idea is that the trip supports the moths and algae that benefit sloths. Others suggest it may help sloths communicate, but the full answer is still being studied.
Worth remembering
- Algae grow in sloth fur, tinting it green.
- Sloth fur hosts moths, beetles and fungi.
- Slowness helps sloths survive on a leaf diet.
In context
Sloths survive on leaves, which are low in energy and hard to digest. They have a slow metabolism, large stomachs with multiple compartments and a body temperature that varies more than most mammals. Moving slowly is part of how they make that diet work.
Being slow and green has another benefit. Predators such as harpy eagles and jaguars hunt by spotting movement. A still, greenish sloth tucked in the canopy is hard to see.
Sloths today are small tree dwellers, but their relatives were not. Giant ground sloths, some as large as elephants, roamed the Americas until about 10,000 years ago.
A closer look
Hanging around
Sloths have long, curved claws that let them hang from branches with little effort. Special tendons lock their grip in place.
They eat, sleep and even give birth while hanging upside down.
Surprisingly good swimmers
Sloths are much faster in water than on land. They use a kind of breaststroke.
This helps them cross rivers and move between islands in flooded forests.
Neck tricks
Three toed sloths have extra neck vertebrae, letting them turn their heads a long way.
That helps them reach leaves without moving their whole body.
Related facts
Another animal with remarkable fur polar bear hair is not white.
More rainforest surprises poison frogs get toxins from their food.
Animals adapted to tough diets camel humps store fat.
For another unusual bathroom habit wombats poop cubes.
Key terms
- Algae
- Simple plant like organisms that use sunlight to make food.
- Xenarthran
- A group of American mammals including sloths, anteaters and armadillos.
- Metabolism
- The chemical processes that turn food into energy in the body.
Myth vs reality
Myth
Sloths are lazy.
Reality
Their slow lifestyle is an adaptation to a low energy diet of leaves, not laziness.
People also ask
Why is sloth fur green?
Algae grow in grooves in the hair, which hold water. The algae tint the fur green.
Do sloths really have moths in their fur?
Yes. Some species of moths live in sloth fur and lay their eggs in sloth dung.
How slow are sloths?
They usually move only a few meters a minute, and spend most of the day resting or sleeping.
How often do sloths poop?
Three toed sloths usually descend to the ground about once a week to defecate.
Are sloths related to anteaters?
Yes. Sloths, anteaters and armadillos belong to a group of mammals called xenarthrans, found in the Americas.
