As Brood X emerges across the eastern U.S., trillions of insects will soon take to the trees, shrilling their mating songs. This group of periodical cicadas, as they’re called, makes up three species and spends 17 years underground. In some areas, all species coexist; in others, one prevails.
Brood X cicadas can be distinguished by looking at the underside of the abdomen. The presence of orange stripes and stripe thickness identify both males and females.
Regardless of the species, every short-lived male and female has the same goal: to find a partner and reproduce. This is where sound comes in. Courting males join together in their calls, establishing chorus hot spots that can attract females as far as a mile away.
This audio clip features a chorus of males of the Magicicada septendecula species that call in strings of short chirps. In the background a few males of other species are also audible.
A chorus of Magicicada cassini is different, with bursts of sound followed by rapid clicks. Each species’ distinctive calls allow females to recognize and mate with males of their own kind, which leads to viable offspring.
Cicadas’ sound apparatus exclusive to males, is made up of two drum-like ribbed membranes, called tymbals. Superfast muscles cause tymbals to buckle inward and release, producing 300 to 400 clicks per second. The sound is amplified by the hollow abdomen that acts as a resonance chamber the way a guitar amplifies string vibrations.
The typical male behavior while perching is to make a few calls, walk or fly a bit, then call again. The sound is altered by the position of the abdomen closer or farther away from the tree.
This intricate mechanism gives males a repertoire of sounds, used in their distinctive chorus, while distressed, or while courting an individual female. Here, a Magicicada septendecim male woos a female, who responds with wing flicks, her way of showing interest.
Encouraged by the response, the male increases the frequency of the call in two stages while approaching the female; the sound continues until they mate.
The female will deposit eggs in tree branches sometime later. The newly born larvae that bury themselves underground are the cicadas we'll be hearing 17 years from now.
Diana Marques and Oscar Santamarina, NGM Staff. Sound: Greg Holmes (three species calling, Magicicada septendecula, Magicicada cassini) and Lang Elliott (Magicicada septendecim)
Sources: John Cooley, University of Connecticut; Dan Mozgai, Cicada Mania; Nahirney, Patrick C. et al. “What the buzz was all about: superfast song muscles rattle the tymbals of male periodical cicadas” Research Communication