Porcupines are rodents with a coat of sharp spines, or quills, that protect against predators. The term covers two families of animals, the Old World porcupines of family Hystricidae, and the New World porcupines of family Erethizontidae. Both families belong to the infraorder Hystricognathi within the profoundly diverse order Rodentia and display superficially similar coats of quills: despite this, the two groups are distinct from each other and are not closely related to each other within the Hystricognathi.
The Old World porcupines live in southern Europe, Asia (western and southern), and most of Africa. They are large, terrestrial, and strictly nocturnal. In taxonomic terms, they form the family Hystricidae.
The New World porcupines are indigenous to North America and northern South America. They live in wooded areas and can climb trees, where some species spend their entire lives. They are less strictly nocturnal than their Old World relatives, and generally smaller. In taxonomic terms, they form the family Erethizontidae.
Most porcupines are about 60–90 cm (25–36 in) long, with an 20–25 cm (8–10 in) long tail. Weighing 5–16 kg (12–35 lb), they are rounded, large, and slow, and use aposematic strategy of defense. Porcupines occur in various shades of brown, gray, and white. Porcupines' spiny protection resembles that of the unrelated erinaceomorph hedgehogs and Australian monotreme echidnas.
The North American porcupine is an herbivore; it eats leaves, herbs, twigs, and green plants such as clover. In the winter, it may eat bark. It often climbs trees to find food.
The African porcupine is not a climber and forages on the ground. It is mostly nocturnal, but will sometimes forage for food in the day, eating bark, roots, fruits and berries, as well as farm crops. Porcupines have become a pest in Kenya and are eaten as a delicacy.