A cicada is an insect of the order Hemiptera, suborder Auchenorrhyncha. There are about 2,500 species of cicada around the world. Cicadas live underground as nymphs for most of their lives, at depths ranging from about 30 cm. In the final nymphal instar, they construct an exit tunnel to the surface and emerge. They then molt (shed their skins), on a nearby plant for the last time and emerge as adults. The abandoned skins remain, still clinging to the bark of trees.