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June 23, 2007

Insects as well as birds have own songs

Houston Chronicle (TX):

Next to bird songs, insect songs are the most common tunes of summer. We often attribute insect songs to crickets, but we may actually hear 42 other species of singing insects in local neighborhoods and parks.

You can learn which insect is singing what song with a new book and accompanying CD, The Songs of Insects by Lang Elliott and Wil Hershberger (Houghton Mifflin, $19.95). The book describes 75 species of singing insects found in the contiguous United States.

Superlative photographs depict clear images of crooning insects along with range maps that describe where each species shows up and sonograms that display a wave profile of each insect's song. A 70-minute audio CD lets us hear what the songs sound like.

Insects famous for their songs include crickets, trigs, katydids, coneheads, shieldbacks, grasshoppers and cicadas. Take the crickets you hear while sitting around a campfire in a nearby state park. Could be the curiously named confused ground crickets. Or listen to the grasshopper's crackling call at midday in your backyard. Probably a Boll's grasshopper.

You may wonder how insects "sing," since they have no vocal apparatus like birds. The book explains that critters like crickets and katydids produce stridulations by rubbing the edge of one forewing called a scraper against a hard bumpy surface called a file on the opposite forewing. The resulting sound comes out as trills, chirps and buzzes.

Grasshoppers rub their hind legs against the edge of their forewings like a fiddler rubbing a bow hard across a violin to produce a raspy sound. Grasshoppers common in neighborhood yards often fly a short distance while emitting a crackling sound and flashing the bright colors of their hindwings.

Cicadas make sounds with organs called tymbals, which contain ribbed structures that vibrate to let forth a euphonious sound. But a cicada chorus at midday can be deafening.

Songs of insects like cicadas generally rise in amplitude during midday sun and drop in amplitude at sundown because insects are coldblooded and depend on ambient temperature to regulate their body heat. Also, many insects raise and lower their wings throughout the day to sharpen or dampen the tenor of their songs.

Male insects sing for the same reason male birds sing — to impress females. A "calling song" attracts female insects to a male's territory, and a "courtship song" serenades her once she arrives.

Some male insects like katydids sing in colonies that counter-sing back and forth across a field. The choruses may gradually build to a crescendo and, as if on cue from a choral director, abruptly stop.

Posted by acapnews at June 23, 2007 12:41 AM

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