On the fourth floor of the Smithsonian’s National Museum of Natural History, behind a door marked “Squirrel Range,” is an array of floor-to-ceiling cases, each covered with a white plywood door. Behind those doors are squirrels. Lots of squirrels. More than 30,000 squirrels.

Arranged in drawers, they look like squirrel Supermen: arms and legs outstretched as if flying through the air, their tails cape-like behind them.

“That’s so we can fit them in the drawers more easily,” explains Richard “Thor” Thorington Jr., the Smithsonian’s curator of mammals, who is showing me around with his research assistant, Paula Bohaska. These stuffed specimens from around the world form a veritable squirrel library and underscore something squirrel researchers like to say: “The sun never sets on the Sciuridae!”

Sciuridae: That is the scientific family these animals belong to. The word comes from sciurus, Latin for squirrel. And from whence does the Latin spring? From the Greek skia (for tail) and oura (for shadow). The squirrel’s name comes from its ability to shield itself from the sun with its tail.

The sun never sets indeed.

There are 278 species of squirrels, living on every continent but Australia and Antarctica. There are ground squirrels and tree squirrels and flying squirrels. Chipmunks are squirrels. Prairie dogs are squirrels. Groundhogs are squirrels. Yellow-bellied marmots are squirrels.

Much of what I know about squirrels I know from talking with Dr. Thorington and from reading his 2006 book, “Squirrels: The Animal Answer Guide,” written with Katie Ferrell. Here is some squirrel trivia sure to wow your friends at parties:

Dino-squirrel. The first squirrels showed up in the fossil record about 36 million years ago.

All sizes. The largest squirrel is the marmot, which can weigh up to 18 pounds. The largest tree squirrel is the handsome Ratufa of Southeast Asia, weighing about 5 pounds. At the other end of the spectrum is the pygmy tree squirrel. The size of a mouse, it weighs less than half an ounce.

Interesting feature. Before DNA analysis made it possible to figure out which types of squirrels were related to one another, Reginald Pocock of the British Museum of Natural History determined that noting differences in the baculum was a good way to classify squirrels. The baculum is the penis bone.

Fancy footwork. Tree squirrels have extremely flexible hind ankles. That’s how they can race up a tree, then turn around and race down it, their toenails clinging to the bark. It would be like you being able to stand on your toes then rotate your feet so your soles faced forward.

Geronimo! Flying squirrels don’t really fly. They use a parachute-like membrane attached to their feet — called a patagium — to glide. They can typically glide at least three times the distance they can drop.

Swimming squirrels. In fall 1933, a Cornell researcher spotted at least 1,000 squirrels trying to swim across the Connecticut River near Hartford. In 2005, a University of Wisconsin professor who was kayaking in Lake Superior spotted a squirrel. He followed it as it swam a mile from the mainland to a nearby island. Wrote Dr. Thorington: “This is the first report of a squirrel swimming in the Great Lakes, as well as the longest reported swim of a North American red squirrel.”

Swarming squirrels. An abundance of acorns and other foods can create an abundance of squirrels. When the food supply drops, hungry squirrels go on the move looking for food. In 1990, thousands swarmed in the Washington area, their carcasses littering roads.

Handy hideout. Tree squirrels, such as the gray squirrels common around here, often have more than one nest. That enables them to bolt for cover should they be threatened by a predator. Incidentally, some squirrel species hibernate but not our gray squirrels.

White out. Although Washington is known for its black squirrels, the town of Olney, Ill., is known for its white squirrels, which are counted annually. (There were 88 white squirrels last fall and 904 gray squirrels.)

Mmm, brains. Squirrels eat more than you may think they eat. “I remember a situation in which a bird was caught and the squirrel was eating the brains,” Dr. Thorington said. “It may have been a chipmunk, but that’s just another kind of squirrel. They’ll take fledglings too. . . . You won’t see birds palling up side by side with squirrels at the feeder.”

Birth control. The aim of every living thing is to perpetuate its DNA. This sometimes means stopping other living things from perpetuating their DNA. At the end of their ejaculation, male squirrels secrete a coagulating agent apparently designed to block the ability of other males’ sperm to fertilize the female, a sort of squirrel sponge. “I’m not sure it does it very successfully,” Dr. Thorington said. Often, the female will simply pull the plug out.

Getting squirrelly

All this week we’re exploring the wide world of squirrels. For more coverage, or to take a video tour of the Smithsonian’s squirrel collection, go to washingtonpost.
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