Written By Tyler Van Fleet.

Posted on September 13th, 2018.

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“What’s that smell?” I thought, as a fresh minty scent swirled into my nostrils. Did this beaver use mouthwash?

On a recent lakeside hike, I stopped in my tracks at the sight of a seriously chewed-up tree. From afar, it looked like something beastly had taken a single big bite out of the trunk. But when I bent down to look closer I saw the familiar chisel marks of beaver teeth. “What’s that smell?” I thought, as a fresh minty scent swirled into my nostrils. Did this beaver use mouthwash?


The chewed tree I knelt by was a black birch (Betula lenta), also known as “sweet birch” for the wintergreen smell and sweet taste of its wood. There’s oil in the inner bark called methyl salicylate that produces a minty flavor. Another compound called xylitol makes it sweet and anti-bacterial. This combination explains why black birch has been a popular source for “chewing sticks” and birch beer over the years.


Had the beaver chewed on this particular tree to enjoy its taste and smell, or HAD it been using mouthwash, in a sense, to help care for its ever-growing teeth? I decided to research beaver diet and health to see if there’s any connection.

Beavers like to eat the leaves, inner bark and twigs of deciduous trees like birch, cottonwood, and willow. They especially like aspen. Fir and pine might get a nibble, but mostly these are chewed so they die and fall down to make room in the woods for more yummy aspen! You might want to brush up on your tree ID skills with MyWoodlot here.


It turns out that aspen bark contains a chemical called salicin that’s similar to the active ingredient in aspirin. Sipping on aspen bark tea can help people reduce pain and sooth stomach aches. So, two of the beaver’s favorite foods – aspen and black birch – have chemicals with human health benefits. Do beavers get the same health boost?

It turns out I’m not the first person to ask this kind of question. There’s a whole new field of science called zoopharmacognosy (from the word roots zoo “animal”, pharma “drug”, and gnosy “knowing”) that explores how animals might self-medicate in different ways to prevent and treat health problems.

You might be familiar with cats and dogs eating grass in order to induce vomiting and get something bad out of their bellies. Lots of other animals do similar things: Bears chew and make a paste out of Osha roots that they smear on their fur as insect repellant; chimps eat bitter leaves to reduce stomach parasites; and wooly bear caterpillars eat certain plant toxins when they are infected by parasites to try and kill them off, just to list a few. Seriously, check out the “zoopharmacognosy” Wikipedia page and prepare to have your mind blown!

I haven’t found any studies that show beavers self-medicate – or provide self-dental care – by eating aspen and birch. I do feel good knowing that it wasn’t a stupid question to ask in the first place! In fact, it’s probably observations just like mine that launched this whole new field of science in the first place. So, pop a black birch chewing stick in your mouth, make your observations and keep wondering “why?”

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