Porcupines are nocturnal vegetarians, but can be active by day.

They eat the inner bark, or cambium, of trees. They will also eat foliage, twigs, bark, leaves, buds, fruits, berries, nuts, flowers, and will sometimes feed in fields.

They move slowly and don't see well. They climb trees to escape predators, but will use their quills if they have to. Porcupines do not shoot their quills. The quills are loosely attached. If attacked, a porcupine slaps the attacker with its tail. Many dogs have ended up with a muzzle full of quills by getting too close to a porcupine. The quills have barbs and will work their way in deeper if left alone. A single porcupine may have 30,000 quills. Quills are modified hairs that have hollow shafts with solid tips and bases. The quills can be up to five inches long. Newborn porcupines weigh more than grizzly bear cubs do at birth.

Their tracks show four toes on the front foot and five on the hind foot. Marks made by the long claws usually show. The heel pads have a pebbly texture. This acts as a non-slip surface and helps them climb trees. Sometimes, a tail drag mark is visible in the trail.

Porcupine scat is in pellet form, and often found in piles at the base of a tree where the animal has been feeding.