11 Fascinating Facts About Beavers

Beavers' ability to shape their environment is beyond impressive—but you already knew about the dam building. Let’s look at some other things that make beavers incredible.

1. Beavers used to be giant.

Although they didn’t have the characteristic flat tail, giant beavers of the Ice Age, in the extinct genus Castoroides, looked remarkably similar to their modern descendants—just much, much bigger. They grew to be up to eight feet long, weighed 200 pounds, and lived a semi-aquatic life.

2. Beavers secrete a goo that smells like vanilla.

In fact, it’s sometimes used in vanilla flavorings. Castoreum is a chemical compound that mostly comes from a beaver’s castor sacs, which are located under the tail. It is secreted as a brown slime that's about the consistency of molasses and smells like musky vanilla. It’s an FDA-approved natural flavoring.

3. Beaver dams can be enormous.

The world’s largest beaver dam stretches for 850 meters in the wilderness of northern Alberta. It was discovered after being spotted on a satellite image in 2007, but scientists believe multiple generations of beavers have been working on the dam since the 1970s. In September 2014, explorer Rob Mark became the first person to ever reach the dam.

4. Beavers are romantics at heart.

Or at least they're monogamous. Dams are usually started by a young male looking for love or by a mated-for-life new couple. A whole beaver family will live in a single dam—mom, dad, young kids, and yearlings.

5. Beavers once traveled by parachute.

In 1948, new human inhabitants of western Idaho began to clash with the local beaver population. The Idaho Department of Fish and Game wanted to put these threatened beavers in a nearby protected area, but they didn't know how to get them there. Elmo Heter of Idaho Fish and Game devised an ingenious solution: By using surplus parachutes from World War II, the department could drop boxes of beavers down from planes. After some careful calibrations, 76 beavers made the skydive into the reserve, and all but one survived the fall.

6. Beavers do not bite off their own testicles.

This one may sound obvious, but up until the 1100s, people thought that beavers did. The myth originated in ancient Egypt and reappeared in the bestiaries of medieval Europe. The story went that beavers knew hunters were after them for the valuable castoreum oil in their testicles. This myth was not terribly difficult to disprove, largely because beaver testicles do not hang outside their bodies.

7. Beavers' front teeth are orange.

And not because they have terrible dental hygiene. To gnaw through tree trunks, they need extra-strong teeth. Fortunately, their tooth enamel contains iron, which makes them incredibly strong, sharp, and orange. Because the orange enamel on the front of their teeth wears away more slowly than the white dentin on the back, a beaver’s teeth self-sharpen as it chews on trees.

8. Dams help beavers avoid ice.

Beavers build dams for myriad reasons, and one is so that the lake behind it will grow deep enough to ensure it doesn’t freeze all the way through during the winter. This bit of temperature control is especially crucial because beavers anchor a food cache to the bottom of the lake to serve as sustenance during the cold months.

9. Beavers’ tails serve multiple purposes.

A beaver’s oversized leathery tail, which can grow up to 15 inches long and six inches wide, has uses both on land and in the water. While swimming, the beaver uses his tail as a rudder or as a siren by slapping it against the water to warn other beavers of a predator. On dry land, the tail acts as a prop to allow the beaver to sit upright or as a counterbalance so he doesn’t tip over while carrying heavy supplies in his teeth.

10. England's beavers have returned after four centuries.

Until recently, the last mention of a beaver sighting in England came in 1789 when a bounty was paid for a beaver head in Yorkshire. By that point, the once-prolific beaver had dwindled due to over-hunting for their valuable pelts and medicinal glands. For a few hundred years, the species disappeared from Great Britain. In the 2010s, conservationists reintroduced a wild population of beavers to a river in Devon and observed how the animals took to their new environment. In 2020, beavers were given legal protection in the UK.

11. Beavers have lots of clever adaptations.

This semi-aquatic mammal has physical adaptations that help them navigate the water. Nose and ear valves shut to keep out water while beavers are submerged, and nictitating membranes (transparent "third eyelids") act as goggles. Their lips close behind their oversized front teeth, allowing beavers to transport building materials and food without drowning.

This post originally ran in 2015 and has been updated for 2021.