This type of bird is a fascinating study, differing in many ways from other bird species. Although there are over 200 varieties of woodpeckers, in general their appearance is quite similar to one another. Four toes on each foot, two facing forward and two backward, allow the bird to grasp the surface of trees easily, and the sharp nails on each of the toes increase their ability to cling. Stiff tail feathers provide stability for the bird. Their bills are straight and sharp; ideal for carving out roosting spots and drilling into surfaces to uncover the hiding places of their prey. During this excavation, dust and bits of wood are kept from being inhaled by the bristly feathers over the nostrils.