The slow-moving North American porcupine is Canada's second-largest rodent (beavers are larger). It is distributed throughout most of the timbered areas of North America. In large males, the body may reach a length of 64.5 cm (25 in.) with the tail adding 14.5 cm (5.5 in). Average weights for males are 5.5 kg (12 lb.) and 4.5 kg (9.9 lb) for females, but individuals have been known to weigh up to 18 kg (39 lb.).
The head, neck and rump are protected by quills. When under attack, the North American porcupine presents its posterior to its adversary and lashes out with its spiny tail. The quills are so lightly fixed to the porcupine's body that they are easily detached and left imbedded in the attacker. The popular notion that porcupines can throw their quills is mistaken.
The tips of the quills are covered with barbs that point backwards, away from the tips. When a quill gets stuck in another animal's skin, the barbs make removing the quills painful and difficult. Porcupine quills are naturally antiseptic; although they can do tissue and organ damage as they travel through the victim, they rarely fester. This is, no doubt, of survival value to the porcupines themselves as they do impale themselves and each other on occasion. Excellent swimmers, the air-filled quills help keep the porcupine afloat.
Fishers are a primary predator of porcupines, but quills have been found embedded in coyotes, cougars, bobcats, foxes, lynxes, bears, wolves and even Great Horned Owls. These predators kill a porcupine by biting its unprotected face or by flipping it over to expose the vulnerable underside.
Primarily nocturnal, North American porcupines are active all year. Their summer diet consists of a variety of shrub and tree leaves. In winter, they feed on the cambium layer and inner bark of trees, and evergreen needles. Their fondness for salt often leads them to roadways where salt has been sprinkled to melt winter ice. Around campsites, they will gnaw on anything smeared with salty sweat, such as canoe paddles, axe handles and saddles.
A porcupine produces one offspring at a time. Young are able to move about quite briskly shortly after birth and, unlike their stolid parents, are quite playful.