The North American porcupine is a large, quill-covered rodent whose dietary habits often lead to misunderstandings, particularly concerning its relationship with trees. A common misconception suggests this animal simply “eats wood,” often due to the noticeable damage left on structures and forest trees. Porcupines are herbivores that consume a wide range of plant materials, but their interaction with trees is far more nuanced than consuming structural wood. Their diet focuses on specific, nutrient-rich layers of living trees, which becomes a necessity during certain seasons. This distinction is essential to understanding the porcupine’s survival strategy.
Addressing the Core Question Wood Versus Bark
Porcupines do not typically consume the hard, structural wood of a tree or logs, but they do feed on the inner bark layer. The part they actively seek is the cambium layer, a thin, soft tissue situated directly beneath the outer bark. This cambium is the growth layer of the tree, and it is rich in sugars and starches, providing a source of concentrated energy and nutrients.
To access this layer, the porcupine must first remove the tougher, less digestible outer bark, leaving behind telltale signs of their feeding. When they strip the bark all the way around the trunk or a branch, a process known as girdling, they effectively cut off the tree’s ability to transport nutrients. This often results in the death of the tree above that point. This behavior is most pronounced in the winter months when other sources of fresh vegetation are unavailable, making the cambium a necessary winter food source.
The True Nutritional Diet
As generalist herbivores, porcupines consume a varied diet that shifts significantly throughout the year based on seasonal availability. During the warmer spring and summer months, their diet is broad, consisting of tender leaves, buds, flowers, grasses, roots, and aquatic plants. They also readily consume fruits and berries when they are ripe and accessible.
The shift to a winter diet focuses on more readily available, but less nutritious, woody materials. In the cold season, porcupines primarily rely on evergreen needles, small twigs, and the cambium layer of trees like hemlock, pine, and spruce. This winter forage is low in nitrogen. Porcupines utilize a flexible physiological strategy to retain nutrients and minimize weight loss during this period of scarcity. They must compensate for the low quality of their food, often feeding heavily on a single tree until the entire crown is consumed.
The Salt and Mineral Connection
The actions that most frequently lead people to believe porcupines “eat wood” are actually driven by a physiological need for sodium and other trace minerals. The porcupine’s natural plant-based diet is often high in potassium but low in sodium, creating an internal imbalance that the animal must correct. This mineral deficiency motivates them to seek out salt-rich materials found outside of their typical forage.
They are known to chew on human-made objects like wooden tool handles, plywood, tire rubber, and even shed antlers. These items attract porcupines because they often contain residual salts from human sweat, road de-icing salt, or sodium-based resins used in manufacturing. Plywood is frequently targeted because of the sodium-based glues used in its construction. This chewing behavior is not for caloric energy but is a direct attempt to satisfy a biological requirement for sodium.