By Donald Lewis
Iowa State University
It's a noisy place out there in the back yard, even after you turn off the mower and the leaf blower, silence the dog and the neighborhood kids, and just stand and listen. It can be a veritable cacophony with all the buzzing, chirping, whirring, zitzing and general insect noise going on.
Why all the noise? Some of that insect noise is communication; that is, individuals are exchanging information. Some of the noises such as mosquitoes buzzing in your ear or flies drowning in your iced tea are incidental to the insect's motion and activity.
In the case of true communication the recipient of the information will do something with that information, such as change behavior. And it turns out that insects have a lot of information to share with each other. They may be recognizing other members of the same species or locating a mate. They may be giving directions to food or warning of danger. Some messages say, "Spread out!" Other messages say, "Come closer."
Insect communication by sound is limited to a few groups of insects. Most accomplish the task by rubbing body parts together. And as some might suspect, it is the males that are making all of the racket, at least in the well-known singers such as cicadas, katydids and crickets.
The annual cicadas start the insect chorus in late afternoon with the ascending zing-zing-zing sound coming from the trees. The common annual cicada in Iowa is the species known as the scissor-grinder, a name that describes the sound made by the vibrating membranes on the sides of the abdomen of the males. The song sounds like someone is pressing scissors against a grind wheel in rapid succession. Even people who aren't familiar with the appearance of these large green insects will remember the empty shells left by the cicadas on tree trunks and fence posts as they transform to the winged, adult stage, as well as the familiar sound they make.
At dusk the male crickets begin rubbing their wings together, dragging a small peg on one wing across a row of ridges on the other. The result is a series of clicks similar to what happens when you click your thumbnail down the teeth of a comb. Only with the crickets the clicks are so fast you don't hear the individual clicks. What you hear is a trill or a chirp. The black field crickets are the kind that get into the house later in the fall, so most people know what those sound like. The tree crickets produce short, perfectly-spaced trills that you hear from a distance all summer long.
Late at night the last singers of the day take over and sing till the wee hours of the morning. Katydids are large green insects (2 -2 1/2 inches in length) that are more commonly heard than seen. Katydids resemble a leaf and easily hide within the upper crown of a hardwood tree. They are named for the rhythmic song they sing in late summer. The males sing in quick bursts of two, three or four notes that sort of sound like Kay-tee-did. Or Kay-tee-did-did. The sound is a crisp and harsh tone similar to saying the word zit with a prolonged Z sound and abrupt T on the end. Now say it three times in quick succession. Neighboring males often alternate their chirps creating a synchronized call-and-response medley pulsating back and forth between tree tops.
Except for the household invasion of the field crickets in late summer, these singing insects are not pests. Some people do complain about the katydids interrupting their sleep, but otherwise all are harmless and do not feed on garden crops, corn, soybeans or forages.
There are several websites on the Internet where you can listen to the sounds of insects. One such site is called "The Songs of Insects" and is part of the Music of Nature series. When finished this site will have songs of birds, frogs and other animals. For now you can enjoy a sample of the insect songs, including the ones mentioned above by connecting to www.musicofnature.com.
The songs of the insects grow slower and slower as temperatures decrease, and they eventually fall silent by October. Alas. Enjoy the chorus while you can.
Donald Lewis, Entomology, (515) 294-1101, firstname.lastname@example.org
Del Marks, Communications and External Relations, (515) 294-9807, email@example.com