Porcupines are vegetarian. In winter, much of their diet consists of needles, twigs and small limbs of evergreens, especially hemlocks. In spring, summer and fall, porkies eat a wide variety of vegetation, including grasses, sedges, and the flowers, leaves, twigs, roots, buds, catkins and seeds of many other plants. In wild areas, porcupines gnaw on shed deer antlers. Closer to civilization, their chewing damages wooden buildings, telephone poles and ornamental trees.
Porcupines crave salt.
They're occasionally seen along highways where salt has been used to melt ice. They're also said to relish the glue in plywood. If a porcupine chews off an isolated section on a tree's trunk, the bark will, in time, close over the wound. If a porcupine girdles the trunk, however, the tree will die. Beech trees are often damaged only at their bases, perhaps because porkies have a hard time climbing this smooth-barked species.