Cicadas are among the most recognizable insects, known for the distinctive, loud sounds that fill the air during warmer months. These creatures spend a significant portion of their lives underground, emerging periodically to complete their adult life cycle. The pervasive buzzing often heard is a biological phenomenon, sparking curiosity about its origins and purpose.
How Cicadas Produce Their Distinctive Sounds
Male cicadas generate sounds using specialized organs called tymbals, located on the sides of their abdomen. Unlike crickets, cicadas use a more complex mechanism: each tymbal is a ribbed membrane made of resilin. Muscles rapidly contract, buckling the membrane inward to produce a click, and relaxing to spring it back. This rapid buckling and unbuckling, occurring 120 to 480 times per second, creates a continuous buzzing sound.
The sound produced by the tymbals is significantly amplified by the cicada’s hollow abdominal cavity, which acts as a resonant chamber. This air-filled space allows the sound waves to bounce around, increasing their volume and carrying them over long distances. The size and shape of this abdominal cavity can vary between species, contributing to the unique sound characteristics of different cicada types. Some species also utilize hollow tubes called tracheae, which are part of their respiratory system, to further amplify their calls.
The Biological Reasons Behind Cicada Calls
The purpose of the loud sounds produced by male cicadas is to attract mates. Each cicada species has a distinct “song” that helps females of the same species identify and locate suitable partners, even amidst the calls of other species. This species-specific acoustic communication is for successful reproduction.
Cicadas also produce other types of calls beyond mating songs. When disturbed or handled, they may emit a loud, squawking sound, known as a disturbance or alarm call, intended as a defensive mechanism. Male cicadas often engage in “chorus calls” where multiple males synchronize their songs. This collective calling creates a much louder sound, which can serve as a super-stimulus to attract more females and potentially deter predators due to the overwhelming noise. These congregational songs are influenced by factors like weather and the calls of other males.
The Auditory Experience of Cicada Noise
Cicada calls are among the loudest insect-produced sounds, capable of reaching high decibel levels. While a single cicada may not be overwhelmingly loud, large groups can create a sustained noise comparable to a lawnmower or motorcycle. Some species, like the African shrill thorntree cicada (Brevisana brevis), can exceed 106 decibels, making them one of the loudest insects in the world. In North America, cicada choruses can reach 80 to 120 decibels at close range, with group averages often around 88.5 decibels.
The characteristics of cicada sounds vary by species, ranging from rhythmic ticks and buzzes to high-pitched whines or musical tones. Periodical cicadas, for instance, have distinct songs, from a rapidly rising buzz to a sustained howl. Cicadas are primarily active during the daytime, with vocal activity peaking in the hottest parts of the day, as warmer temperatures enhance their metabolic rate.
While individual cicadas live for only a few weeks as adults, the noisy period of an emergence can last four to six weeks. The sheer volume of cicada noise has even led to confused residents contacting emergency services.