Tymbal

Tymbal (or timbal) is a term for a corrugated exoskeletal structure used to produce sounds in insects. In male cicadas, the tymbals are membranes in the abdomen, responsible for the characteristic sound produced by the insect. In tiger moths, the tymbals are modified regions of the thorax, and produce high-frequency clicks.

The paired tymbals of a cicada are located on the sides of the abdominal base. The "singing" of a cicada is not stridulation as in many other familiar sound-producing insects like crickets (where one structure is rubbed against another): the tymbals are regions of the exoskeleton that are modified to form a complex membrane with thin, membranous portions and thickened "ribs". These membranes vibrate rapidly, and enlarged chambers derived from the tracheae make the cicada's body serve as a resonance chamber, greatly amplifying the sound. Some cicadas produce sounds louder than 106 dB (SPL), among the loudest of all insect-produced sounds. They modulate their noise by positioning their abdomens toward or away from the substrate.