02 April 2021
The largest rodent in North America and competes with its Eurasian counterpart, the European beaver, for being the second-largest in the world, both following the South American capybara. The European species is slightly larger on average but the American has a larger known maximum size.
The beaver is semiaquatic. The beaver has many traits suited to this lifestyle. It has a large, flat, paddle-shaped tail and large, webbed hind feet. The unwebbed front paws are smaller, with claws. The forepaws are highly dextrous, and are used both for digging, and to fold individual leaves into their mouth and to rotate small, pencil-sized stems as they gnaw off bark. The eyes are covered by a nictitating membrane which allows the beaver to see under water. The nostrils and ears are sealed while submerged. Their lips can be closed behind their front teeth so that they can continue to gnaw underwater. A thick layer of fat under its skin insulates the beaver from its coldwater environment.
The beaver’s fur consists of long, coarse outer hairs and short, fine inner hairs (see Double coat). The fur has a range of colors, but usually is dark brown. Scent glands near the genitals secrete an oily substance known as castoreum, which the beaver uses to waterproof its fur. There is also another set of oil glands producing unique chemical identifiers in the form of waxy esters and fatty acids. The lush, workable fur was made into a number of products, most notably hats. Demand for furs for hats drove beavers nearly to the point of extinction, and the North American species was saved principally by a sudden change in style.
The beaver possesses continuously (or endlessly) growing incisors, and is a hindgut fermenter whose cecum, populated by symbiotic bacteria, helps to digest plant-based material. These traits are not unique to beavers, and are in fact present among all rodents. Nonetheless, the beaver is remarkably specialized for the efficient digestion of its lignocellulose-heavy diet.