15 Fascinating Facts About Otters

Light brown otter with closed eyes and an open mouth

Stephen Meese / Shutterstock

Charismatic otters star in memes, greeting cards, and puns (You "otter" know).  These semi-aquatic mammals catch our attention with expressive faces and their antics—sliding down riverbanks, juggling rocks, and cracking open crabs while floating on their backs.  No less than 13 species of otters live in waterways on five continents. The only places without endemic otters are Australia and Antarctica. All species are IUCN Red Listed, and only one is included as "least concern." Learn 15 more facts about these fascinating mammals.

1. Sea Otters Hold Hands While Sleeping

pair of otters on their backs in water holding hands

Peter Burka / Flickr / CC BY-SA 2.0

Sea otters sometimes hold hands while they're sleeping to keep from floating away from each other. Often a mother and pup will hold on to each other while they are resting so that they don't drift off from each other. This sometimes carries over to adult otters. Sea otters also sleep on their backs, wrapped in long strands of kelp. They use the kelp as an anchor while sleeping so they can nap without the worry of floating out to the open ocean.

2. Otters Aren't All Sea Otters

river otter facing camera looking angry with mouth open

Mark Medcalf / Shutterstock

River otters are frequently mistaken for sea otters. Size and location are generally give-aways for telling otter types apart. River otters live primarily in freshwater, though they do swim and hunt in seawater. Sea otters live exclusively in the ocean along the coastline. Sea otters are significantly bigger than most river otter species. River otters have visible ears, swim belly down, use webbed feet to paddle, and move swiftly on land and water. Sea otters move clumsily on land, eat while floating on their back, and paddle with hind feet and tail.

3. Otters Are in Trouble

Seven otters on rocky shoreline alternating between being on all fours and standing on hind legs

Anna Moskvina / Shutterstock

Of the 13 species of otter, IUCN lists five as endangered, five as near-threatened, two as vulnerable. Only the North American river otter is a species of least concern.

In areas with strong enforcement of endangered species and anti-pollution laws, some species of otters are making remarkable comebacks. Numerous threats to otters still exist, including pollution, overfishing, and poaching for pelts, and the illegal pet trade is a significant problem in Southeast Asia.

A cat parasite, toxoplasmosis, threatens otters as well. Found in cat feces, it enters waterways through feral cat fecal runoff and flushable cat litter. The parasite lays eggs in invertebrates that the otters then eat.

4. Otters Have Many Names

Otter pup on rocky shoreline

Henk Bentlage / Shutterstock

Baby otters usually are called pups. They can also be called kits or kittens. Female otters are sows, and males are boars.

Otter groups have a variety of names. They are called a family, bevy, lodge, or, as their energy level might suggest, a romp. Romp is the most common term for a group of otters on land. A group of otters in the water is called a raft.

5. Giant River Otters Live Up to Their Name

Giant otter on partially submerged log.

ostill / Shutterstock

The giant otter is an endangered species found in South America, primarily along the Amazon river and the Pantanal. It is the longest of the otter species. Giant otters grow to as long as 6 feet and weigh as much as 75 pounds. They have a serious appetite to match their size and activity — eating up to nine pounds of food each day.

Poaching for their velvet-like fur caused a significant population decline. Threats also include habitat degradation, pesticides, pollution from mining, and even conflicts with fishers who consider the species a competitor. Experts estimate that fewer than 8,000 exist, though pinning down a more exact number is hard.

6. Hairy-Nosed Otters Are a Lazarus Species

Hairy Nosed Otter with long white whiskers standing on the rocky side of a pool

Rigelus / Wikimedia Commons / CC BY-SA 4.0

Hairy-nosed otters are a small species found in Asia. They are so rare; the species was considered extinct until 1998 when small populations were discovered. This rediscovery, after presumed extinction, makes them a "Lazarus species." Despite finding populations of these otters, the remaining population is under threat through habitat loss for palm oil and other agriculture and capture for the illegal wildlife trade.

7. Some Species Lack Claws

Otter with no claws facing a second otter on a rock

Targn Pleiades / Shutterstock

Most otters have sharp claws at the end of each toe, which helps them to grab prey. However, there are three species of otter that have blunt or no claws. Their common species names are give-aways: Asian small-clawed otter, African clawless otter, and the Congo clawless otter.

These species also have less webbing between their digits. This, along with the shorter claws, allows them to have greater dexterity in using their paws to feed on small prey.

8. They Have Noteworthy Poop

Family of Eurasian river otters (Lutra lutra) sprainting on high point. The spraint is a method of marking territory and high points are a favoured location, even those washed by tides.
Fotosearch / Getty Images

Otter droppings are called "spraint." The spraint is full of fish bones from their sizeable diet, but surprisingly researchers describe it as smelling like "violets" or "jasmine tea." Otters have a latrine area where area otters go to do their business. These latrines not only serve as a place to relieve themselves; they use them to communicate.

Otters perform a "scat dance" where they stomp their hind feet before lifting their tail and leaving their spraint. Sea otters have such rapid digestion that their spraint floats. Otters also excrete something called "anal jelly," a mucusy goo containing secretions from anal glands and shed intestinal linings.

9. Sea Otters Have the World's Thickest Fur

sea otter grooming itself

Doug Meek / Shutterstock

Sea otters don't just have the densest fur of all otters — they have the densest fur of all animals! They have as many as 2.6 million hairs per square inch. They need every last hair because they are the only marine mammal without a blubber layer as insulation against the freezing ocean water. Their fur protects them from the cold and keeps them waterproof. Each day they spend five hours grooming their thick hair.

10. All Otters Eat A Lot

otter eating a fish

Kjersti Joergensen / Shutterstock

A hefty appetite isn't unique to giant otters. River otters eat around 20% of their body weight each day. Sea otters eat from 20-33% of their body weight each day.

To get enough to eat, otters spend around five hours each day foraging. They use loose skin under their front limbs as pockets to hold their prey and rocks while they return to the surface to eat. When ready to eat, the otter will use the rocks as tools to open the hard shells of mollusks and shellfish.

These hefty appetites help keep the aquatic environment in check. For example, as part of their diet, sea otters eat the urchins that feed on kelp. Without sea otters, urchin populations boom, kelp disappears, and the many other species that depend on the kelp forests.

11. They Are Keystone Species

Otter head peeking out of the water, swimming with discarded plastic bottle

Derek Keats / Flickr / CC BY 2.0

Just as sea otters are linked to a kelp forest's health, so too are river otters linked to the health of riparian habitats. River otters need clean water, healthy stream banks, and an abundance of prey, so they are susceptible to river systems' disruptions.

When otters disappear, something is off-kilter in the ecosystem. It may indicate an increase in pollutants, a loss of prey due to habitat destruction, bacterial overgrowth, or habitat fragmentation along waterways.

Because otters are at the top of the food chain, any pollutants in the environment become concentrated in their bodies. Additionally, their high caloric means they are also susceptible to decreasing populations of prey. While otters aren't migratory in a typical sense, they emigrate to other waterways if there is a prey shortage.

12. Otter Mothers Have a Lot of Work

mother otter grooming pup

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Scientists believe sea otters only have a single pup because of the amount of time and energy they take. Pups cannot swim at all for their first month, despite being born in the open sea. Their fluffy fur, keeps them warm and traps air and allows them to float, but only if it is clean. Mother otter must groom her pup in addition to herself. When leaving the pup to hunt, the mother otter blows air into the clean fur to create buoyancy similar to a life jacket. Then she wraps the pup in a blanket of kelp to anchor it until she returns.

Sea otter pups have intense nutrition needs and nurse for six months. Mother sea otters must spend up to 14 hours per day foraging to support herself and her pup. This high demand leaves otter mothers depleted and unable to fight even minor illnesses—many die.

13. They Take Over Other Animal's Homes

Otter standing on fallen tree

aabeele / Shutterstock

When an otter doesn't build its own home, it takes up residence in abandoned beaver lodges or muskrat dens. In fact, sometimes otters will move in even when beavers are still living in the lodge, taking up residence in areas that the beavers aren't utilizing.

Otters will also take over the dens of foxes, badgers, and rabbits as long as the holes are dug near enough to river banks. Their resting spots, called a hover or a couch, are usually little more than a bed of reeds. Otters also use what's called a holt. Holts are small underground dens where otters can escape danger, take shelter, and where females raise their young.

14. They Are Speedy Swimmers

Underwater shot of otter swimming

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It should be no surprise that otters are great swimmers. But how great are they? They can swim faster than the fastest humans. Otters can hold their breath for 3-4 minutes at a time while they swim and can swim at speeds of 7 miles per hour. Otters have powerful, somewhat flattened tails perfect for propelling themselves through the water.

River otters have webbing between their toes as well. They can close their nostrils and ears to keep out water and have sensitive whiskers to locate prey even in the murkiest water.

15. Their Play Puzzles Researchers

Otter juggling rocks

Magnus Hagdorn / Flickr / CC BY-SA 2.0

Otters have a reputation for play, but researchers remain puzzled by certain behaviors. Few animals play as adults, and otters are one of them. The playful sliding on a riverbank could be marking territory and efficient locomotion. More often, research shows it because it is fun. Scientists thought rock juggling was to practice hunting skills or efficient extraction of meat from shells. Instead, researchers learned, they are more likely to juggle rocks when hungry or bored. Young otters and old otters most often juggle rocks.