porcupine, member of either of two rodent families, characterized by having some of its hairs modified as bristles, spines, or quills. The quills are loosely attached to the porcupines' skin and pull out easily, remaining imbedded in any predator that comes in contact with them. The New World, or tree, porcupines (family Erethizontidae) are slow-moving, more or less arboreal animals. The ends of their quills bear minute overlapping barbs; when imbedded they are very difficult to pull out and tend to work inward, piercing internal organs. The North American, or Canadian, tree porcupine, Erethizon dorsatum, is found in wooded areas over most of North America, excluding the SE United States. This animal has a coat of long, shaggy, brown or black hair mixed with shorter quills. When threatened it erects its quills and backs toward its enemy, delivering a blow with its tail. Even if no contact is made quills may fly out; this has given rise to the erroneous belief that porcupines can shoot their quills. North American porcupines spend the day, singly or in groups, in rock cavities, hollow logs, or burrows. At night they forage in trees, feeding on leaves, buds and bark. They subsist in winter entirely on bark stripped from evergreens. The damage they do to trees is conspicuous, but seldom fatal. The Central and South American tree porcupines, species of the genus Coendou, have naked-tipped, prehensile tails, with which they hang from branches. Also called coendous, they are up to 20 in. (50 cm) long, including the tail, which is as long as the body. The Old World porcupines (family Hystricidae) have no barbs on their spines. The larger species belong to the genus Hystrix, and are found in scrubby areas in Asia, Africa, and SE Europe. These animals are unable to climb trees. They have extremely long black-and-white-striped quills on the hind part of the back and on the tail; some species also have crests of long bristles on their heads. The rest of the coat is a mixture of bristles or spines and short hair. The tail quills are hollow and are used to make noise; when the animal is alarmed it erects its quills and rattles its tail. If attacked it runs backwards into its enemy, leaving the attacker full of quills. It forages at night for roots and other plant foods, scuffling and grunting as it moves about. Old World porcupines dig deep burrow systems, where a number of them may live in adjoining burrows. Members of most species weigh 50 to 60 lb (23–27 kg); despite their large size they can move swiftly when alarmed. Species of several other genera, smaller and possessing spines or bristles, but no quills, are found in Africa and SE Asia; these are good tree climbers. Porcupines are classified in the phylum Chordata, subphylum Vertebrata, class Mammalia, order Rodentia, families Erethizontidae and Hystricidae.