While no living animal subsists on a diet of entire trees, many different animals eat individual portions of trees. For example, animals such as deer, elephants and giraffes consume a large quantity of leaves and fruit, but little else. By contrast, termites are one of the few animals in the world that are capable of digesting the woody part of trees, known as the xylem.
In addition to large mammals, many arboreal mammals consume the leaves, fruit and flowers of trees. While few birds consume leaves, a great many birds eat the fruit and seeds that come from trees, including blue jays, sparrows and cardinals. Many birds, particularly woodpeckers, also eat the insects and invertebrates that live within the wood of trees. Insects also eat a great number of tree leaves. Insects such as locusts, grasshoppers or leaf hoppers can quickly strip a tree of all of its leaves. Additionally, many caterpillars subsist on the leaves of fruit trees.
Termites eat xylem, but they typically do not eat living tissue. Because they are one of the few animals capable of extracting the energy found within xylem tissue, termites are a very important component of all ecosystems. Without termites, ecosystems would fill up with too many dead trees.