Young porcupines nurse about two months, but begin feeding on vegetation after only the first few days of life. Young usually stay with the female through the summer and then are on their own. Coloration of young porcupines usually darkens with age, and they reach full adult size in three to four years. While very nearsighted, porcupines have keen senses of smell, hearing and touch. The porcupine has 30,000 or more quills, which cover all its body except the snout, throat, belly and feet pads.
Quills are modified hairs with hollow, spongy centers.
The loosely attached quills easily embed in attackers upon contact. While the porcupine does not throw quills, the flailing muscular tail and powerful body may help impel quills deeply into attackers. The quills' barbed ends expand with moisture and continue to work deeper into flesh. Porcupine quills have mildly antibiotic properties and thus are not infectious. Quills may cause death if they puncture a vital organ or if a muzzle full of quills leads to starvation.