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Why do beavers eat wood?


Author: Layal Bou Abdo MNS

Illustration: Angeline Boswell

There are two living species of beaver:
The North American beaver (Castor canadensis) and the Eurasian beaver.
  • North American beavers weigh between 35 and 65 pounds (15-29 kgs) and are 23 to 39 inches (60 to 100 centimetres) long. The tail adds another 7.75 to 12 inches (20 to 30.5 cm) to its length, according to National Geographic.
  • The Eurasian beaver (Castor fibre) is smaller than its North American cousin. They usually weigh from 29 to 77 pounds (13 to 35 kg) and are 29 to 53 inches (73 to 135 cm) in length. Their tails are narrower, and skulls are smaller than those of the North American beaver.
Beavers eat Wood
Beavers are semiaquatic animals. They can run on land, but their greatest skill is in water. They are as fast as 6 miles per hour due to their webbed feet and their flat scale-covered tail (paddle-like). Moreover, their tail allows them to steer and move through the water. They slap their tails on the water to show danger. Beavers can stay underwater for about 15 minutes. In fact, their large lungs allow them to stay underwater for an extended period of time.
Beavers have a robust body that helps them conserve heat for harsh winters and cold weather. These remarkable tails also serve as fat reserves to aid them through winter. Beavers slap the tail on the water for warning others.
Beavers’ teeth are golden-orange because they are rich in iron. This protective coating of enamel makes their teeth strong. Beavers have long incisors (20-25mm) that grow continuously throughout their life. Despite that, beavers incisors trim down because they use them to cut trees. The way the teeth wear away is uneven. This gives the incisors a chiselled shape, which helps beavers cut through hard objects like wood.
The teeth in the back of their mouths or the molars are flat and white. Beavers use their back teeth to grind the food. If beavers don’t wear their teeth down over time they can actually starve. In other words, they will not be able to close their mouths and grind their food with their molar teeth. Beavers, in fact, eat with their mouths closed behind the incisors.
Beavers do not eat wood! In fact, they cut trees to form dams and lodges but eat the tree bark or the softer layers of wood underneath. Beavers have unique micro-organisms in their guts that help them digest as much as 30 percent of the cellulose they eat from plants. These herbivores also eat leaves, woody stems and aquatic plants.
They have clever ways to make sure there is food available all year long. Beavers also store branches on the muddy pond floor beneath their lodges. Thus, they can eat during the winter when they spend most of their time inside. The cool water acts like a fridge, keeping the stems fresh and preserving their nutrients.
Beavers are very dexterous and tend to hold their food between their front paws to eat.

Why do beavers build dams?

Beavers eat wood! Beaver Den
Beavers are nature’s engineers! They change their habitat! Beavers use mud and rocks to build watertight dams made of woven sticks, reeds, branches. They chose their location based on the sound of flowing water.
The dams form slow-moving ponds that reduce stream erosion. As a result, this provides a brand new habitat for small fish and other aquatic wildlife. Also, this protects the beavers from invading predators. Beavers build dams to create wetlands (lands that do not drain well). These wetlands produce perfect food for beavers. Most Dams are 5-10 meters long.
Beavers have dexterous front feet allowing them to be experts in holding objects. They also build lodges. These dome-like lodges are often constructed away from the shore. They form islands that can only be accessed from the water. A lodge can have many underwater entrances and many passages to various rooms. Beavers even make a sort of chimney or skylight when they build their lodges, to allow fresh air in. The walls are insulated. The floor of the lodge is often covered in wood shavings to absorb moisture and provide a comfortable place to sleep.
The lodges are homes of beavers. This is the place where they live, give birth, raise their young and store food. They can be up to 6 feet high and as wide as almost 40 feet!
Beavers are nocturnal animals, they become active at night. Their vision is poor; they take cues from the sun and use their whiskers to detect things. Beavers must be able to find objects in dark water and other dim areas such as their lodges. Their eyes have a special membrane that covers them while they are swimming underwater. With transparent membranes over their eyes, beavers can see very well under the water. Beaver’s ears contain valves that shut when they go underwater, and they have good hearing.
They are hard workers and operate 26-29 hours /day. Beavers stay busy in the fall gathering food for the winter.
On their behinds, at the base of their tails, beavers produce a goo that smells like Vanilla. Castoreum is a chemical compound that mostly comes from a beaver’s castor sacs. It is secreted as a brown slime that’s about the consistency of molasses and smells like musky vanilla. It is used for communication and to mark their territory, and this oil makes the fur waterproof. 
For hundreds of years, the castoreum was used as a flavour enhancement to flavour food and drinks. And in some places, it is found in perfume and processed food as a natural flavouring substance. The castoreum has a medicinal property.  It is rich in Salicylic Acid, which is a major compound to form aspirin. That’s because of the beaver snacks on the bark of willow trees that contain the chemical Salicin.

Why are beavers important for the environment?

Beavers are so important in ecology. They are so important for every plant and animal that lives in their space. Dams alter the flow of rivers and can flood hundreds of acres into wetlands. Dams prevent erosion and purify water. They keep the water cleaner when fine sand collects like a clay above older dams. Microbes (good germs), in beaver wetlands, break down toxic elements in the water. Beavers create homes for many animals like frogs, salamanders, turtles, fish, ducks, otters, owls and insects. They provide nesting for some species of birds.

Fun Facts!

Beavers have a special toe that has a double toenail and allows beavers to comb their fur?

Beaver’s claws are sharp and efficient at digging?

Beavers will gnaw on trees until they fall! Beavers can fell as many as 300 trees in a year! They are capable of felling an 8-foot tree in 5 minutes?

Human is the biggest predator for beavers? Humans threaten beavers by trapping for fur pelts and their castor oil. Humans also, pollute water in the beavers’ environment and destroy beaver habitats.

The biggest beaver dam in the world is in Canada Wood Buffalo National Park? It’s more than 850 meters long, and scientists believe multiple generations of beavers have been working on since the 1970s. It was discovered after being spotted on a satellite image in 2007. In September 2014, explorer Rob Mark became the first person to ever reach the dam.

Beavers used to be giant? Giant beavers of the Ice Age, known as “Castoroides,” looked very similar to the beavers we know today—just much, much bigger. They grew to be up to 8 feet long and 200 pounds and lived a semi-aquatic life. Although, they didn’t have a flat tail though!

Beaver is romantic in the heart! A whole beaver family will live in a single dam—mom, dad, young kids.

Beavers once travelled by parachute! What??!! In 1948, inhabitants of western Idaho began to clash with the local beaver population. Consequently, the Idaho Department of Fish and Game decided to use surplus parachutes from World War II, and drop boxes of beavers down from planes in a nearby protected area. All 76 beavers but one made the skydive into the basin.

We are certain your kid asks you health (human & animal) questions that genuinely leave you stumped! Leave a comment below and we are happy to answer “why” in future blogs.
Copyright © 2020 Little Medical School Ottawa


  1. Ted Uhlman on January 11, 2021 at 10:29 am

    Mistake on the beaver page. They are hard workers and operate 26-29 hours /day.

    • lmsottawa on January 11, 2021 at 3:24 pm

      Hi Ted,
      Thanks for the comment. You are right, this is not well explained. We have put a hyperlink on the source. The hard working beavers work 26-29 straight hours


    • Laura Bodman on August 7, 2022 at 8:17 pm

      I caught that too! Lol Maybe they work so hard that it FEELS like that many hours. Lol

  2. Calvin on September 8, 2021 at 3:38 am

    We have a shallow well 17ft deep. The beavers with their dam holding back water in the marsh keeps the pressure on the shallow aquifer so our well doesn’t dry up. Just got thru tossing a few apples out to him!

  3. […] Rodents and rabbits’ incisors grow continuously, so they require regular gnawing to keep their teeth at a healthy length. […]

  4. […] Beavers do not eat wood! In fact, they cut trees to form dams and lodges but eat the tree bark or the softer layers of wood underneath. Beavers have unique micro-organisms in their guts that help them digest as much as 30 percent of the cellulose they eat from plants. via […]

  5. Are Beavers Good For A Pond? – Bescord on May 28, 2022 at 9:01 pm

    […] Beavers do not eat wood! In fact, they cut trees to form dams and lodges but eat the tree bark or the softer layers of wood underneath. Beavers have unique micro-organisms in their guts that help them digest as much as 30 percent of the cellulose they eat from plants. via […]

  6. Jaime on November 11, 2022 at 2:36 pm

    amazing tree falling at park, employees quickly wrapped fencing on remaining planted cottonwood. we brought remaining logs closer to water and were 1 night they were bucked up and removed.

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