The beaver is a large, semi-aquatic rodent that significantly impacts the ecosystems it inhabits across the Northern Hemisphere. Beavers are the second-largest living rodent species in the world, surpassed only by the South American capybara. There are two distinct species: the North American beaver (Castor canadensis) and the Eurasian beaver (Castor fiber). These animals are renowned for their ability to modify their environment through complex dam and lodge construction.
Typical Size and Weight
Adult North American beavers typically weigh between 24 and 65 pounds (11 to 30 kilograms), with an average weight often cited around 40 pounds (18 kilograms). Their body is stout and chunky, adapted for conserving heat and pulling heavy loads. The head-to-body length of a mature beaver usually measures between 24 and 40 inches (60 to 102 centimeters). When measuring total length, the tail adds a significant dimension, bringing the overall length up to or sometimes exceeding four feet.
Distinguishing Physical Features
The tail is a large, horizontally flattened oval paddle covered in scales and sparse hair. An adult tail typically measures 10 to 18 inches (25 to 45 centimeters) long and about 4 to 5 inches (10 to 13 centimeters) wide. This appendage is used as a rudder for steering while swimming, a prop for balance while cutting wood, and serves as a fat storage area for energy reserves during winter.
The large incisor teeth are another defining physical characteristic. These four chisel-like front teeth are long and continue to grow throughout the animal’s life, which counteracts the constant wear from gnawing on wood. The intense orange color of the incisors comes from iron compounds within the enamel, making the teeth exceptionally hard and resistant to cracking or decay.
Comparing the Two Species
The Eurasian beaver (Castor fiber) is generally considered slightly larger and heavier on average than its North American counterpart. Eurasian beavers typically have a head-to-body length ranging from 31 to 39 inches (80 to 100 centimeters). Adult Eurasian beavers often weigh between 24 and 66 pounds (11 to 30 kilograms), though some sources record a wider range up to 84 pounds (38 kilograms). The Eurasian species also tends to have a narrower tail and a more elongated skull structure than the North American beaver.
Maximum Recorded Size
Exceptional individuals can grow significantly larger, particularly the North American species. The maximum reliably recorded size for a North American beaver is 110 pounds (50 kilograms), documented in 1921 in Wisconsin, United States. For the Eurasian beaver, an exceptionally large specimen was recorded at 70 pounds (31.7 kilograms), although it is reportedly possible for the species to exceed 88 pounds (40 kilograms). These maximum sizes are typically reached by very old individuals, as beavers continue to grow throughout their lives, surpassing the typical weights of most mature adults.