Wood You Eat That? An Overview of Beaver Teeth and Digestive System

By: Michael Allen Bryden

There's no denying that beavers do some pretty amazing things, not least their ability to adapt to their environment, as well as forcing their environment to adapt to them. By creating dams, beavers engineer their ecosystem around themselves: not just benefiting their own lifestyle but the lives of many other animals around them. If you love your lake or your wildlife, you have to love the beaver because they are the reason lakes and wetland levels are maintained in the highlands of Ontario! Without the beaver, few soils and basins would exist to keep water on our landscape. The beaver would not be able to do all of this with... their teeth!

A beaver’s diet in the summer consists of leaves, buds, twigs, aquatic vegetation; and the bark of deciduous trees, which make up nearly 50% of what they eat. In the winter months, their diet consists almost entirely of woody material that they stored under the ice in a storage section known as a cache. With the help of a very specialized tool (their teeth), beavers are able to accomplish amazing feats such as the construction of their dams and lodges, as well as the consumption of these woody materials. 

More specifically it is a beaver's four front incisors that the stars of the show in the wood gnawing process. To begin, their incisors are long and separately spaced on the dental arch: this arrangement makes it possible for beavers to possess a second layer of lips behind the incisors, which acts as a barrier to protect them from swallowing water while carrying building material during a swim. Regarding the make-up of the teeth themselves, beaver teeth are remarkably unique. Unlike in humans, where the outermost layer of the tooth –known as enamel– is hardened calcium, a beaver’s enamel is hardened with iron. This makes a beaver’s teeth far stronger in comparison and gives them a rusty orange colour. As they age, their teeth continue to grow and sharpen from all the chewing.

Not only are beavers capable of chewing through trees, but they also have a specialized digestive system to go with it. To understand how beavers are able to digest the nutrients found within tree bark, we first have to undergo a quick biochemistry and anatomy lesson. Unlike cells found within animals, plant cells are surrounded with structural layers known as cell walls. They are often rigid and very difficult to digest. The cell walls are composed of carbohydrate polymers, cellulose and hemicellulose, and an aromatic polymer, lignin. Lignocellulose is composed of the three previously mentioned molecules and makes up a large component of a beaver's diet. 

The digestive systems of herbivorous animals can either be a single saclike compartment (monogastric), or subdivided into various complex chambers (digastric). Monogastric herbivores, such as beavers, possess a single-chambered stomach where molecules such as lignocellulose can be digested. Monogastric animals that are able to digest these cellulosic materials are known as hindgut fermenters. This process is aided by microorganism fermentation in the intestine, which, in the beaver's case, takes place in a modified cecum. Humans, like many other animals, possess a cecum, but in beavers, it is an enlarged pouch located at the beginning of the large intestine connecting the small intestine to the rest of the large intestine. A beaver’s cecum contains enzymes derived from bacteria and fungi to help break down the tough cellulose molecules found in woody plants. To ensure they digest as many nutrients as possible from their meal, the beaver partakes in a method known as coprophagy, where the individual eats their own feces to run the food through their digestive system several times. This process might be gross by human standards, but it is an example of highly adaptive strategy that allows beavers to thrive on a specialized diet.

The ways that beavers interact with their habitat are varied, incredible, and teeth-dependent. Their dam- and lodge-building are regular feats of engineering; their ability to alter ecosystems to suit their needs is second only to humans; and their diet is based on a food source with notoriously inaccessible nutrients: beavers tackle all of these with apparent ease, and big buck teeth.