Can Sloths Swim? Why These Slow Animals Are Good Swimmers

How do sloths swim?

A swimming sloth looks a little like a person doing a slow breaststroke or doggy paddle. It reaches forward with its long front limbs, pulls back through the water and pushes along with smaller movements of its hind legs. The head and face stay above the surface, so the animal can breathe and see where it is going.

Sloths have several features that help in water:

• Long arms: the front limbs of three-toed sloths are about half as long again as the hind limbs, giving each stroke a long reach.
• Buoyancy: a sloth’s large stomach is full of fermenting leaves, which, together with its light build, helps it float.
• Pulling muscles: sloth muscles are built for slow, steady pulling, the same motion that powers their swimming.
• Water-shedding fur: the long hair grows from belly to back, the reverse of most mammals, so water runs off when the sloth hangs upside down in the rain.

Are sloths faster in water than on land?

Yes. On the ground, a sloth is almost helpless. Its legs are made for hanging, not standing, so it drags itself forward with its claws at only a few meters a minute. In water its weight is supported, and its arms can work freely.

Estimates of swimming speed vary, but sloths have been reported to swim at roughly 13 m (44 ft) a minute, several times their speed on the ground and faster than their usual pace through the trees. That is still only about 0.8 km/h (0.5 mph), but for a sloth it counts as fast. You can read more about their famous slowness in why are sloths so slow?

Why do sloths swim?

Sloths live in tropical forests laced with rivers, streams and seasonal floods, so water is part of their world. A brown-throated sloth may swim to:

• Cross rivers and streams that block the way to new feeding trees or a mate.
• Move through flooded forest in the Amazon, where water can stand among the trees for months during the rainy season.
• Reach a new territory when a young sloth leaves its mother’s home range.
• Escape danger by dropping from a branch that hangs over the water.

Swimming carries its own risks. Caimans and large snakes such as anacondas hunt in the same rivers, and a sloth in open water has nowhere to hide.

How long can a sloth hold its breath?

The most often quoted figure is that a sloth can hold its breath for up to 40 minutes. The idea is that a sloth can slow its heart rate and already low metabolism even further when underwater, so it uses very little oxygen.

This number appears in many books and websites, but it is based on limited observations rather than careful studies of wild sloths, so it should be treated as an estimate, not a proven record. What is clear is that sloths are comfortable in water and can stay calm while swimming for long distances.

Swimming sloths through history

Swimming has played a big role in sloth history. Fossils show that ancient sloths reached many Caribbean islands, probably by swimming or drifting across stretches of sea. On the Pacific coast of what is now Peru and Chile, a group of extinct sloths called Thalassocnus went further still. Over millions of years they became adapted to wading and feeding on seagrass in shallow coastal waters.

Today the best example of an island sloth is the pygmy three-toed sloth (Bradypus pygmaeus). It lives only on Isla Escudo de Veraguas, a small island off the Caribbean coast of Panama, where it was cut off from the mainland when sea levels rose thousands of years ago. It lives mostly in red mangroves at the island’s edge and is listed as Critically Endangered on the IUCN Red List, making it one of the rarest mammals in the Americas.

Two-toed and three-toed sloths in water

Both groups of living sloths can swim. Three-toed sloths, including the brown-throated sloth, are often described as especially capable swimmers, and they are regularly seen crossing rivers in Central and South America. Two-toed sloths, such as Hoffmann’s two-toed sloth, also swim when they need to, but they tend to be more agile on the ground and may walk or climb around obstacles more often.

If you see a sloth swimming in the wild, the best thing to do is watch quietly from the bank or a boat at a distance. Pulling a swimming sloth out of the water is stressful for the animal and is not needed: it knows where it is going.