WINTER COATS
Some species pile on the layers, like the Arctic musk ox, whose soft undercoat—called qiviut—insulates them from -50 degree Fahrenheit temperatures. Polar bears have an extra layer of fat to keep toasty.
Others grow thicker fur in the fall, like white-tailed deer, and some even grow lighter coats to blend into the snow, Sharon Chester, author of The Arctic Guide, Wildlife of the Far North, says via email.
North American mammals such as the Arctic fox, least weasel, Arctic hare, and ermine have this adaptation, Chester says.
The camo works if snow is consistent, Chester says, but it's tougher if snow arrives late and melts early—which is happening more due to global climate change. A 2016 study reported snowshoe hares in Montana that were mismatched to their environment experienced a 7 percent decrease in survival rate.
Wood frogs, which range from the southeastern U.S. to the Arctic Circle, "hunker down in some leaf litter and freeze solid" into a "frogcicle," says Greg Pauly, curator of herpetology at the Natural History Museum of Los Angeles County.
The Arctic ground squirrel, or siksik, can drop its body temperature below freezing while it's hibernating. This is likely due to another process called supercooling, in which the body temperature can go below the freezing point without forming ice.