(Intro)

They're one of the largest rodents in the world, they're indisputably adorable and hey, Canada doesn't put just anyone on their money. But the main reason you should appreciate beavers is that they're second only to us in their ability to completely transform the environments they live in. Usually for the better though.

While we like to surround ourselves with Warehouse stores and hamburger restaurants, beaver will turn a stream-fed meadow, even a patch of desert, into a lush, watery habitat for all sorts of wildlife; aquatic and land-lubber alike.

They do it but of course by building dams, and darn can these guys dam! Most beaver dams are 5 to 10 meters long and form small ponds behind them, but sometimes these structures have been known to turn into decades-long development projects.

The biggest beaver dam in the world, in Canada's wood buffalo national park, is more than 850 meters long, forming a huge wetland that's actually been photographed from space. It's actually been under construction since the 1970s with subsequent generations of beavers adding to it and it's getting bigger every year.

Beavers go through all the trouble of dam building primarily for defense. Some build lodges built of sticks and mud in the ponds that they create, whilst others burrow into their muddy banks. Both are designed to be entered only underwater. By surrounding themselves with deep water, beavers can protect their dens from predators like wolves and wildcats, while creating a habitat that supports the aquatic plants that they like most, like cattails, willows, pond weed and aspen. 

The dams are usually started by single males trying to attract a mate, or a young couple which pair up for life. Adorable beaver love. But one thing that's a little less cute is how completely serious these guys can be about their dams. Scientists call it instinctive behavior but it can end up looking kinda compulsive. Biologists believe that the sound of running water actually triggers dam-building behavior in beavers. Some theorize that beaver may even be able to feel or otherwise sense in the water when a leak has sprung in a dam. Research has shown that little gaps and tension created in beaver dams will cause every member of a colony to drop everything to repair it regardless of what else needs to be done.

Scientists, a little evil, have even run audio recordings of water running near beaver sites and have returned in the morning to find speakers covered with sticks and mud.

This obsessive engineering is all made possible by beavers trademark teeth, and you may have heard that their teeth continue to grow throughout their lifetimes which is true, but only their big curved front incisors.

Beaver's voluminous tree gnawing keeps their teeth from growing too long, but they don't actually eat through trees. They actually prefer to feast on non-woody plants like waterlilies and cattails in the spring. In winter they strip trees of their bark and eat the soft layer of tissue underneath known as cambium, and despite what the cartoons have taught us, beaver's famous front teeth are not white, they're orange, because their tooth enamel contains iron which makes them incredible strong and sharp, even though it makes them look like they have a 2 pack-a-day habit.

And finally, a note about beaver butts. They smell... delightful, Both male and female beavers have a pair of anal scent glands that they use to mark their territory, and the yellowish oil that they produced, called castoreum, smells precisely like sweetened vanilla. So much so that for 100s of years it was used to flavor food and drinks, and in some places can still be found in perfumes and processed foods under the ambiguous moniker of 'natural flavoring'.

Other cultures have prized castoreum for it's medicinal properties, and that might be because of one beaver's favorite snacks is the bark of willow trees, which contains the chemical salicin which people have used for centuries to make natural painkillers.

But because beavers eat so much of the bark, their sweet-smelling butt oils can be chock full of salicylic acid which is the precursor compound to aspirin.

Now what other animal can you think of that makes its habitat more livable, drops everything to keep its neighborhood safe, and has a bum that smells like dessert?

I can't come up with anything.

Thanks for watching this week's SciShow though, and if you'd like to learn more about all kinds of animals check out our partner channel Animal Wonders at youtube.com/anmlwndrs, there's a link in the description,  and don't forget to go to youtube.com/scishow to subscribe so you can keep on getting smarter.