The porcupine (Erethizon dorsatum) is a large-bodied, slow-moving rodent who would be ill-equipped to avoid any sort of predator were it not for his unique natural defensive system. This animal's 30,000 quills, which are actually specially modified hairs, are marvels of evolutionary adaptation and present from birth.

Contrary to popular belief, porcupines cannot impale people, or their pets, by "throwing" their quills through the air. While quills are indeed formidable, they can only do so much to help these near-sighted, often clumsy animals protect themselves. An attacker must actually come into contact—however slight—before a porcupine's quills can dislodge and imbed themselves. Suffice it to say that unless porcupines are provoked, no harm is likely to come from these otherwise benign and appealing creatures.

Porcupines range throughout Canada and the western United States, into northern Michigan and Wisconsin, and in New England, New York, and Pennsylvania in the East. Males and females are about the same size; a full-grown porcupine is about 2 to 2 ½ feet long and weighs up to 30 pounds. Porcupines are nocturnal, and are most commonly found in coniferous or evergreen forests but also range into deciduous woodlands.

Porcupines are strict herbivores, feeding almost entirely in trees. During the winter they favor the woody parts of plants, especially the inner bark of trees. The bark stripping or "girdling" that occurs when a porcupine has worked on a tree occurs on both the trunk and upper limbs and is fairly distinctive. During the warmer months, porcupines will nip off the ends of branches to get to the leaves, buds, nuts, and fruit; these nipped branches may litter the ground beneath porcupine trees. Virtually all species of trees found within a porcupine's range are eaten, while preferences may vary regionally or even individually.

Breeding occurs in the fall and is followed by a gestation period of about 210 days. This is unusually long for a rodent—almost five times longer than that of squirrels. Young porcupines are born in the spring—females almost always bear just one—and their soft quills harden within hours of birth. Much humorous speculation is traditionally associated with the act of mating in porcupines, but in truth it's no different from most mammals. Although porcupines are normally sedentary, deliberate creatures, males can sometimes get quite aggressive with one another during the breeding season. But that fuss is all done without the use of the most formidable weapon in their arsenal, the quills.

The quills are indeed the hallmark of these animals. A sheath of muscle controls quill movement so that they can be raised in a sign of warning when a porcupine is threatened. Porcupines often back up towards their attackers, the better to lash out with their heavily-quilled tails. Stressed porcupines may also produce a noxious odor and chatter or clack their teeth to tip off would-be assailants.