Nature Notes: Tree crickets are regularly heard in late summer but rarely seen

I enjoy the insect chorus heard through our open windows, and late-summer evenings are best.

The populations for many of the music producers are at their peak. The activity of the nighttime singing crickets is in full swing by 8 p.m. or soon afterward.

How does the cricket "sing"? It starts with the upper set of its two sets of wings. These front wings have tiny ridges like those of a file on their underside, with a thickened area, like a scraper, on the edges. The cricket moves its wings rapidly from side to side, rubbing them across each other so that they vibrate and make a rasping noise — the chirp. Female crickets don't sing, but they listen with eardrums near their knees.

Temperature has a great deal to do with the way a cricket behaves. The same applies to other insects. Since July 22, we have been hearing the enchanting sound of the snowy tree crickets in Waconia and the whole Twin Cities area. Last year I heard the first ones singing July 27.

The snowy tree cricket, a relative of the black field cricket, is also called the temperature cricket because it is an accurate thermometer. Commonly heard but seldom seen, the cricket chirps more times per minute in warmer temperatures than cool. To produce their music, the males raise their wings above their backs and vibrate them rapidly from side to side. The females are silent. Males often sing in a chorus. If the sound seems to be coming from all around, it often is. Snowy tree crickets chirp with a shrill tuneful and persistent "chee-chee-chee," also described as "waa-waa-waa." "Treat-treat-treat," a sleigh bell-like sound, can sometimes be heard, too. If you count the number of chirps in 15 seconds and add 40, you will have a good approximation of the air temperature in degrees Fahrenheit.

You may catch sight of this shy, pale-green creature, hardly an inch long, if you carefully use a flashlight and look into a shrub. Its "music" has been famously described as "the sound of moonlight."

Jim Gilbert's Nature Notes are heard on WCCO Radio at 7:15 a.m. Sundays. His observations have been part of the Minnesota Weatherguide Environment Calendars since 1977, and he is the author of five books on nature in Minnesota. He taught and worked as a naturalist for 50 years.