Beavers are often seen felling trees, leading many to believe they consume wood. However, they do not eat wood. They chew and cut down trees for specific purposes, not as a food source.
What Beavers Actually Eat
Beavers are herbivores with a diet primarily consisting of softer plant materials. Their favored food source is the cambium, a highly nutritious, soft inner layer beneath the bark. They strip away this thin layer after felling trees, leaving behind debarked logs and branches. Beavers also consume a variety of other plant parts, including leaves, twigs, buds, and the roots of woody plants.
Their diet also includes a significant amount of aquatic vegetation, such as water lilies, cattails, sedges, rushes, and pondweeds, particularly during warmer months when these are abundant. During the fall, beavers stockpile branches and logs underwater near their lodges, creating a food cache for winter when other fresh vegetation is scarce. This allows them to access food even when ponds are frozen.
Why Beavers Chew Wood
Beavers chew wood primarily for two reasons: constructing their dams and lodges, and maintaining their continuously growing incisor teeth. The trees they fell, often softwoods like aspen, willow, and birch, provide the raw materials for their aquatic structures. Beavers use branches, sticks, mud, and rocks to build dams across streams, which create the deep, still ponds necessary for their survival and protection from predators. Their lodges, built within these ponds, offer a secure living space with underwater entrances.
Chewing also serves a biological purpose related to their teeth. Beaver incisors grow continuously throughout their lives, sometimes by as much as 4 feet per year. Chewing on wood helps wear down these long, chisel-like front teeth, preventing them from overgrowing. Their teeth, with iron-hardened enamel on the front and softer dentin behind, allow for self-sharpening as they gnaw, maintaining an efficient cutting edge.
How Beavers Digest Plant Material
While beavers chew wood, their digestive system is not equipped to break down the tough, lignin-rich woody fibers. Instead, they are specialized to digest cellulose, a complex carbohydrate found in the softer plant materials they consume. Beavers are hindgut fermenters; the primary site for microbial digestion occurs in an enlarged section of their digestive tract called the cecum, located at the beginning of the large intestine.
Within the cecum, a diverse community of symbiotic bacteria produces enzymes, such as cellulases, which are capable of breaking down cellulose into digestible nutrients. This microbial fermentation process allows beavers to extract energy from the plant cell walls of their diet.
Beavers can digest approximately 30-33% of the cellulose they ingest, a rate comparable to some ruminant mammals. To maximize nutrient absorption, beavers sometimes re-ingest their own feces, a process called coprophagy, allowing the food to pass through the digestive system again for further breakdown by their gut microbes.