In forestry and natural history, a snag is a standing dead tree. In a forest ecosystem, they provide habitat for insects and tree cavity dependent wildlife: dead or decaying wood is easier to dig a hole in. Snags also are useful for feeding: most snags show evidence of use by insectivorous birds, probably because snags are great places for immature or migrating insects to hide. Snags also allow more light into the forest floor, allowing the growth of shrubs and grasses, increasing the variety of habitat in a forest. In a mature mixed forest, snags make up 5 to 10 percent of the trees.