The arrival of cicadas, often marked by their loud, buzzing chorus, is usually accompanied by a strange visual phenomenon. Scattered across tree trunks, fences, and garden walls are numerous empty, insect-shaped casings. These discarded husks are a common sight during a mass emergence, sparking curiosity about what they are and why they are left behind. Finding one of these shells is a direct sign that a major biological transformation has just occurred nearby.
The Specific Term for the Shed Shell
The technical term for what is commonly called a cicada shell is exuvia, with the plural form being exuviae. This term applies to the shed outer layer of any arthropod, including insects like the cicada. The exuvia is essentially the cast-off exoskeleton of the cicada’s juvenile form, known as the nymph.
The shell is largely composed of chitin, a tough, flexible material that provides structure and protection. The cicada exuvia retains the intricate detail of the nymph, including the large, distinctive forelegs used for digging underground. The shell is typically a brittle, translucent brown color and preserves the shape of the head, eye casings, and tiny hairs. The most telling feature is the large, vertical split that runs down the back, which is the precise opening the adult cicada used to pull itself free.
The Molting Process and the Cicada Life Cycle
The cicada shell is shed as part of the insect’s final transition from its subterranean existence as a nymph to its winged adult form. The nymph spends years underground feeding on tree root fluids, growing steadily. Since the rigid exoskeleton cannot stretch, the insect must grow a new, larger exoskeleton underneath the old one multiple times throughout its life.
The final shedding, known as ecdysis, occurs after the mature nymph digs its way out of the soil and climbs a vertical structure. Once securely positioned, the nymph anchors itself and begins the slow process of forcing its body out through the split on its back. This action allows the soft, pale adult to emerge. The new adult then clings to the empty exuvia as its wings expand and its new outer layer hardens, preparing it for its brief life above ground.