A cicada shell is the exoskeleton from which a winged, adult cicada emerges. Once the exoskeleton is shed, it is left behind, attached to a bush or a tree branch.
There are at least 2,500 species of cicada. Cicadas grow and develop underground, sucking sap from plant and tree roots. When their growth is complete, mature nymphs tunnel out of the ground and attach to vegetation.
Some species surface annually. Periodic cicadas are those that appear every 13 to 17 years. In years in which periodic cicadas emerge, large quantities of abandoned shells can be found on branches and twigs.
Cicada shells are valued as an ingredient in traditional Chinese medicine. These medicines are often used as fever reducers and to treat skin conditions and other ailments.