Extension Communications
3614 Administrative Services Building
Ames, Iowa 50011-3614
(515) 294-9915
8/30/99
Contacts:
Donald Lewis, Extension Entomology, (515) 294-1101,
drlewis@iastate.edu
Elaine Edwards, Extension Communication Systems, (515)
294-5168, eedwards@iastate.edu
Yard and Garden Column for the Week Beginning Sept. 3
Katydids and Other Choristers
By Donald Lewis
Extension entomologist
Iowa State University Extension
The sound of insects can be the sound of music, or it can be the most irritating thing you've ever heard. It depends a lot, I guess, on where the insects are and your mood at the time.
From late summer through fall is the prime time to hear several common and well-known noisy insects. The field crickets are chirping, the cicadas are buzzing, the tree crickets are trilling and the katydids are rasp-rasp-rasping from the treetops.
Insects use noise (that is, sounds) to transfer or exchange information. The chirps and buzzes are all audible expressions of an important message being sent from one member of a species to another member of the same species for the purpose of producing a desired reaction by the receiver.
It all sounds rather stuffy when written that way. It is much more agreeable to think the buzzing and chirping insects are performing for our enjoyment. However, we are merely eavesdroppers on some exciting and high-level negotiations.
Insect Communication
Production of sound is only one of the ways insects communicate. A great deal of insect communication is visual. For example, the colors of butterflies are reflected light with meaning beyond the beauty we perceive. Color, form, pattern, intensity and movement can all be part of a coded message being sent like ship-to-ship semaphore signals. The romance of fireflies is not just for us to enjoy. The males producing most of the light on a summer night have much more important intentions.
The most common form of insect communication is chemical signaling. Chemicals that carry messages between members of the same species are called pheromones. Specialized glands on one insect produce the pheromone and specific receptors on the receiving insect intercept the volatile molecules to decipher the intended meaning.
With so much special "equipment" to produce, send and receive messages, you can bet those messages are important. Some messages are life saving. Others are life perpetuating. Messages passed between insects can be as simple as, "This way to the food." Or, "This is a good place to hide." Some messages communicate danger. The most important (and interesting) messages involve the sex life of insects. Sex messages are loaded with subtext and subtleties such as, "I'm the same species." "I'm the opposite gender." "I'm available." "Please reply!"
Sound Production
Insect sounds or acoustical signals are produced in several ways. The cicadas ("locusts") that have been buzzing in the trees from mid-afternoon to evening since July produce their sound by drumming. Two membranes located along the sides of the male's body are vibrated by strong muscles located within the abdomen. The vibrations produce high&endash;pitched rapid buzzes that are resonated through air sacs to control sound volume and quality. The upward angles of the wings form a megaphonelike chamber that further controls the sound.
Other insects produce sound by rubbing or scraping body parts against each other (stridulation). Crickets and katydids, for example, rub together the front wings. A sharp edge at the base of one wing is pulled across a filelike ridge on the other wing. The resulting sound of this "file and scraper" arrangement is a series of clicks similar to the noise made by dragging your thumbnail along the teeth of a comb. However, crickets and katydids move their wings so fast that we are unable to hear individual clicks. Instead we hear a chirp or rasp composed of dozens or hundreds of closely spaced clicks delivered in short bursts.
Katy Did or Katy Did Not
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 male's song comes in a quick burst of two, three or four notes that can be sung as "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 individuals often alternate their chirps creating a synchronized call-and-response medley pulsating back and forth between treetops.
Katydids are native to the United States from the East Coast to Nebraska. Although they eat the leaves of trees and shrubs they are not of any economic importance. The female uses her flat swordlike ovipositor at the tip of her abdomen to deposit eggs into plant tissue in the fall. The eggs wait through the winter and the nymphs emerge the following spring.
Meanwhile the songs of aging adults grow slower and slower as temperatures decrease, and they eventually fall silent by October.
Alas. Enjoy the chorus while you can.
ml: isugarden
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