<P> The most distinguishing feature of the porcupine is its coat of quills . An adult porcupine has about 30,000 quills that cover all of its body except its underbelly, face, and feet . Quills are modified hairs formed into sharp, barbed, hollow spines . They are used primarily for defense, but also serve to insulate their bodies during winter . Porcupines do not throw their quills, but when threatened, they contract the muscles near the skin which causes the quills to stand up and out from their bodies . When the quills are in this position, they become easier to detach from the body, especially when the porcupines swing their tails towards attackers . The barbs at the tip become lodged in the flesh of an attacker and are difficult and painful to remove . The quills are normally flattened against the body and in this position are less easily dislodged . </P> <P> The North American porcupine has a strong odor to warn away predators, which it can increase when agitated . The smell has been described as similar to strong human body odor, goats, or some cheeses . The odor is generated by a patch of skin called the rosette, on the lower back where modified quills serve as osmetrichia to broadcast the smell . The characteristic odor comes from the R - enantiomer of delta - decalactone . Not present is the S - enantiomer which smells like coconut and is used in flavorings and perfumes . </P> <P> North American porcupines range from Canada, Alaska, and into northern Mexico . They are commonly found in coniferous and mixed forested areas, but have adapted to harsh environments such as shrublands, tundra, and deserts . They make their dens in hollow trees or in rocky areas . </P> <P> During the summer, they eat twigs, roots, stems, berries, and other vegetation . In the winter, they mainly eat conifer needles and tree bark . Porcupines are selective in their eating; for example out of every 1,000 trees in the Catskill Mountains, porcupines will only eat from 1 - 2 linden trees and one bigtoothed aspen . </P>

Where are porcupines found in the united states
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