Beavers: Castoridae

Beavers are among the largest of the rodents. They have a combined head and body length of 31 to 58 inches (80 to 140 centimeters). The flat, paddle-like tail is about 9.8 to 17.7 inches (25 to 45 centimeters) long. The tail is broad and scaly. A typical beaver can weigh 33 to 75 pounds (15 to 33 kilograms), with a few beavers weighing in at 100 pounds (45 kilograms). Males and females are similar in size.

Beavers' bodies are stocky with short limbs. Each limb has five clawed digits. The back feet, which are larger than the front, are webbed. The claws on the hind feet's first and second toes are split, appearing as a double claw. They have long, curved incisors, chisel-shaped teeth at the front of the mouth, that are an orange-brown color. The incisors grow continuously.

Their eyes are small and their ears are short. Their ears are set far back on their heads, which are broad and rounded. Beavers can close both their ears and nostrils when underwater. Beavers have a skin fold inside their mouths, which allows them to grasp onto items in their teeth without water entering their throat.

Beavers' fur is dense, made up of a fine coat of soft fur, called underfur, beneath long guard hairs, coarse hairs that form the outer fur and protect the underfur. The short underfur helps the beaver with water shedding and insulation. Fur color is a glossy yellowish brown to black. Their bellies are slightly paler in color, ranging from a brown to yellowish brown. The tail and feet are black.

The family name "Castoridae" refers to beavers' castor glands, or "castors." A gland is a group of special cells that make substances so that other parts of the body can work. This pair of glands, along with a pair of anal glands, releases a pungent, musky odor. Both sets of glands lie at the base of the tail.