Heavy-bodied, solitary, slow-moving, nocturnal rodent with quills (modified hairs) along the back, tail, and, on certain crested species, the neck and shoulders.
The quills are easily detached when touched. The New World species (four genera in family Erethizontidae) are arboreal and have barbed quills; the Old World species (four genera in family Hystricidae) are terrestrial and have unbarbed quills. The North American porcupine ( Erethizon dorsatum ), about 31 in. (80 cm) long with a tail about 12 in. (30 cm) long and quills about 3 in. (8 cm) long, drives its powerful tail against an assailant. For food, it favours the tender tissue beneath tree bark. Crested porcupines, the typical Old World porcupines, run backward, quills erect, into the enemy. They eat roots, fruit, and other vegetation. The African crested porcupine, the largest terrestrial rodent in Europe and Africa, may weigh 60 lb (27 kg) and have quills 14 in. (35 cm) long.