I stepped out of the car this morning in River Forest and was greeted by this awesome sound. Cicadas were everywhere. First I noted the thousands of former slumbering holes next to the bushes where I parked. Then I saw them on the bushes, curled and clinging. Some torpidly flew through the warm air while others, less fortunate, lay squashed on the sidewalk.
At lunch I sat outside to enjoy their collective sound which is like a police siren without any edges, one sustained note ripe with urgency. According to the Smithsonian National Museum of Natural History (where the above sound sample was found):
The sound is made with structures known as tymbals which are located on the sides of the first abdominal segment, near the top just behind where the hindwings attach. Large muscles contract, causing the tymbal surface to bend inwards which produces a vibrating click. These vibrating clicking noises are enhanced by a large air chamber that extends well into the abdomen. Repeated contractions by thousands of cicadas can create a spectacular din.
After lunch I returned to the library where I sat to a curiously hearty crunch. One of the critters journeyed in on my posterior and had met its demise.