Periodical cicada: mechanism of sound production.

The species Magicicada septendecim and Magicicada cassini of the 17-year cicada produce sound by sequentially buckling a series of stiff ribs embedded in a flexible tymbal. Each such collapse excites a damped oscillation in a resonant cavity. By this means the cavity (an abdominal air sac) is excited 10 to 12 times per muscle contraction, which permits a normal muscle to perform a task requiring very rapid repetitive activity.