These furry inhabitants of the Arctic tundra are one of the most iconic, recognizable species in the world. But how much do we really know about polar bears? They're powerful predators that are easily equipped for the weather. But they face frightening threats from melting sea ice and an ever-dwindling habitat.

Here's just the tip of the iceberg about what makes these well-loved bears so fascinating.

Polar bears are actually black — not white

Although polar bears appear white, their fur is actually translucent, according to the WWF-UK. It only seems white because it reflects light, providing camouflage in the snow. Underneath all that fur, polar bears have black skin. That helps them absorb the sun's warming rays, points out National Geographic, keeping them warm in bitter temperatures.

They're built for cold weather

polar bear shaking off water Polar bears are built to withstand their icy cold and wet habitats. (Photo: Riekus/Shutterstock)

They spend their lives on the ice and in the cold, and they are dressed for it. Polar bears have dense, insulating fur that covers a warming layer of body fat. That layer can be almost 4.5 inches (11.4 centimeters) thick. The layer of fat is what keeps them warm when they're in the water, says Polar Bears International. And it's also why mama bears are reluctant to let their cubs swim in the spring: The babies just don't have enough body fat to stay warm.

Polar bears are classified as marine mammals

Because they depend on the ocean for their food and their icy habitat, polar bears are the only bear species to be considered a marine mammal. That means they're grouped with seals, sea lions, walruses, whales and dolphins, and they also fall under the Marine Mammal Protection Act. But they're still bears.

They are talented swimmers

polar bear swimming Polar bears can swim at a pace of up to six miles per hour. (Photo: Fotokon/Shutterstock)

These big mammals are very graceful in the water. According to the WWF, they can swim at a sustained pace of six miles per hour and can do so for long distances. They use their slightly webbed front paws to paddle, while holding their hind legs out flat like rudders.

Sometimes polar bears are spotted swimming hundreds of miles away from land. They likely didn't get there paddling the entire way, says National Geographic. Instead, they probably hitched a ride some of the way by floating on sheets of ice.

Even though they are strong swimmers, polar bears can get in trouble when storms kick up during these long swims. They've been known to drown when they're far from land in turbulent waters.

They really, really love seals

Polar bears spend about half their time hunting, and seals are mostly what's on the menu. Specifically, they look for ringed and bearded seals because they're high in fat and that's what polar bears need to survive. They hunt by looking for areas of cracked ice, waiting for seals to near the surface of ice to breathe. They use their strong sense of smell to locate them. They often have to wait for hours or days, and their hunts are often unsuccessful.

That's why they will also scavenge whale carcasses and look for other food sources like bird eggs and walruses, reports the National Wildlife Federation. They are at the top of the food chain in the Arctic and have no predators other than humans and other polar bears.

Polar bears can be loners

They spend much of their lives alone except in a few situations like when a female is raising her cubs, when couples are mating or when several bears are all attracted to some food, like a whale carcass, says the National Wildlife Federation. Although adult bears often like to be loners, young polar bears will play with each other.

Their origins are murky

For years, researchers believed that in order to survive in extreme environments, polar bears evolved from brown bears over the last 150,000 years or so. They believed that climate change forced the polar bear to evolve rapidly to adapt to living in the Arctic.

But findings from another study published in the journal Science suggest that polar bears didn't descend from brown bears. After studying DNA from polar bears, brown bears and black bears, researchers believe that the brown bear and polar bear have a common ancestor but the lines split some 600,000 years ago.

Polar bears are huge

huge polar bear sprawled on ground A male polar bear can weigh as much as 1,700 pounds. (Photo: SoWoW/Shutterstock)

Polar bears are about 7 to 8 feet long and about 4 to 5 feet tall at the shoulder when on all four legs. A large male bear can weigh more than 1,700 pounds and can be as tall as 10 feet while standing on his hind legs. A large female can weigh up to 1,000 pounds. They live an average of 25 to 30 years in the wild.

They have many names

Science knows the polar bear as Ursus maritimus, but around the world, the iconic species has plenty of interesting monikers, reports Polar Bears International. Names include Thalarctos, sea bear, ice bear, Nanuq, isbjorn, white bear, beliy medved, lord of the Arctic and white sea deer.

Norse poets called the bear a white sea deer, the seal's dread, the rider of icebergs, the whale's bane and the sailor of the floe. They said the bear had the strength of a dozen men and the wit of 11. The Sami or Lapp indigenous people from northern Europe called the bears God's dogs or old men in fur coats. They refused to call them polar bears out of fear of offending them.

They are in danger of going extinct

polar bear on ice Polar bear population numbers are diminishing due to melting ice. (Photo: Karen Ford Photo/Shutterstock)

In 2008, polar bears were the first vertebrate species to be listed under the U.S. Endangered Species Act as threatened due to predicted climate change. Internationally, they are listed as a vulnerable species by the International Union for Conservation of Nature (IUCN). Canada classifies polar bears as a species of special concern under the National Species at Risk Act.

IUCN estimates that there are fewer than 26,000 polar bears worldwide. Their numbers are shrinking due to habitat loss and melting sea ice. When ice is lost, they have to travel longer distances to find stable ground, which can be a serious threat to their survival. Less ice also means fewer seals to eat.

Mary Jo DiLonardo covers a wide range of topics focused on nature, health, science and anything that helps make the world a better place.

10 fascinating facts about polar bears
From the color of their skin to their amazing swimming ability, polar bears are full of surprises.