Lignophagia

Lignophagia is the abnormal behaviour of chewing and eating wood. It has been recorded in several species, but perhaps most commonly in horses where it is sometimes referred to as "wood chewing". Lignophagia is a type of eating disorder called pica in which normally non-nutritive substances are chewed or eaten. For some animals, wood is the normal primary food source; such animals are known as xylophagous.