How can cicadas, which are small, make such loud sounds? asks a reader.It wouldn't be midsummer without the dog-day cicadas, their plaintive chorus rising and then dying away. Then there are the waves of 13- and 17-year cicadas, which make their deafening appearance in late spring. Cicadas can be as noisy as kitchen blenders, and almost as annoying.
Cicadas are the loudest insects known. Why all the racket? Most cicada sounds are all about the mating. Cicadas have only a short window to find a partner and create a new generation of nymphs before their life above-ground is over. So when you hear a cicada chorus so loud you're prompted to shut your window, think "speed-dating."
How can something so small (the average North American cicada measures less than 2 inches) make a sound so earsplitting?
It's not that cicadas have big mouths. In fact, it's all about the abs. Male cicadas are the singers, and they make the noise using a pair of ridged membranes in their lower abdomens, called "tymbals."
A cicada pulls in its ab muscles around the tymbals, causing them to cave in like a struck drum. The sound resonates in the cicada's mostly empty abdominal cavity, like a resounding note in a concert hall. The cicada's angled wings form a natural megaphone, enhancing the sound further as it exits. And we hear a noise that can reach 80 to 90 decibels, as loud as a vacuum cleaner or lawnmower.
There are more than 2,500 cicada species around the world, each with its distinctive calls and songs. In North America, male 17-year cicadas make at least five categories of sounds.
Ever hear a cicada make a short, harsh buzz as you approach? Entomologists call that an alarm call; males make it when they feel threatened. Then there's the calling song, which attracts other cicadas to a group chorus (often in the highest tree branches). The calling song often consists of one to three calls separated by several seconds of silence.
Many years ago, a man leaving for a date with flowers and candy was said to be "going courting." But it's not flowers, candy or a high salary that attracts female cicadas. It's the sound of his court call that will win a male cicada a mate.
A Court 1 call is similar to a calling song, with shorter gaps between calls. A male makes this sound when he has settled down from his flying and branch-pacing and is trying to woo a nearby female cicada. Court 2 calls are continuous; a male makes this noise as he strolls up to a friendly female. Court 3 calls are a series of quick buzzes. Males make this noise just before they mate. And while flirting female cicadas don't have hair to flip, they do flick their wings, making a come-hither rustle or pop in response to a male's noisy overtures.
To learn more about cicadas and to hear their courting songs, visit http://www.ummz.lsa.umich.edu/insects/index.html
For more cicada sounds and videos, see www.mechaworx.com/Cicada/cicadavideos.asp.
