After 17 years of living underground, the cicadas from Brood X emerged in areas of the US spanning 15 states and the District of Columbia. Brood X is the largest cicada brood with as many as 1.5 million cicadas emerging per acre of land, which puts its total population into the trillions of insects. While all Brood X cicadas will probably look the same to us, Brood X is composed of three species of cicadas, Magicicada septendecim, Magicicada cassinii, and Magicicada septendecula. In cicadas, only the males sing, and the males from these three species each have a distinctive song that will only attract the females from their own species. Thus when you hear a large amount of cicadas singing, the noise is a mixture of three different songs.
The cicadas make their song with a specialized stiff ribbed organ called the tymbal, which is located just next to the site where the wings are attached to the body. The ribs of the tymbal are caused to buckle in sequence by the action of muscles in the insect’s body, and every time one of the ribs buckles it produces a clicking noise. When the clicking noises of the tymbal are produced at a high frequency, it becomes a buzz which is amplified by abdominal air sacks increasing the intensity of the sound. The song of the cicadas can be really loud, approaching the 100 decibel range, and can be heard from a mile away. Because of this, cicadas have to protect their ears from their own sound! Cicadas hear through two large eardrum-like membranes called “tympana” which are connected to the brain auditory centers through a tendon. When the cicada sings, the tendons retracts creasing the tympana to prevent it from being damaged by the sound.
In the video below, you can hear the chorus of cicada sounds made by Brood X at the Seneca Creek State Park in Maryland.
The photograph belongs to the author and can only be used with permission.