Woodpeckers are chiefly known by their characteristic behavior. Most woodpeckers forage for insects on trees and branches by drumming with their beak. Some species will vary their diet with fruits, birds' eggs, small animals, and tree sap. They nest and roost in holes that they excavate in trees. They have four toes on each foot. Two toes point forwards and two point backwards aiding in grasping and climbing trees. They have strong bills for drilling and drumming on trees. They also have a sticky tongues for extracting food. They have an undulating flight pattern consisting of a series of rapid flaps followed by a swooping glide.