What IS that overpowering hum?


Kitty Smith, Texas Master Naturalist, Indian Trail Chapter

 All over Texas in summer the air is pulsing with the overpowering hum of the Cicada. Males produce this species-specific noise with vibrating membranes on their abdomens. The cicada is also a proficient ventriloquist, making it hard to locate the actual source of the noise. Cicadas are members of the order Homoptera. Often two or three inches in length and with a wing spread of 4 inches or more, cicadas are among the giants of the order. They are physically distinguished by their stout bodies, broad heads, clear-membrane wings, and large compound eyes.

Tymbal (or timbal) is the term for a corrugated exoskeletal structure used to produce sounds in insects. In male cicadas, the tymbals are membranes in the abdomen, responsible for the characteristic sound produced by the insect. The paired tymbals of a cicada are located on the sides of the abdominal base. The “singing” of a cicada is not stridulation as in many other familiar sound-producing insects like crickets (where one structure is rubbed against another). The tymbals are regions of the exoskeleton that are modified to form a complex membrane with thin, membranous portions and thickened “ribs”. These membranes vibrate rapidly, and enlarged chambers derived from the tracheae make the cicada’s body serve as a resonance chamber, greatly amplifying the sound. Some cicadas produce sounds louder than 106 dB, among the loudest of all insect-produced sounds. They modulate their noise by positioning their abdomens toward or away from a hard surface.

Cicadas are also famous for disappearing entirely for many years, only to reappear in force at a regular interval. There are some 3,000 cicada species, but only some share this behavior (the 17-year Periodical Cicada (Magicicada Septendecim) is an example). Others are called annuals because, they appear every year. The Dog Day Cicada, for example, emerges each year in mid-summer.  For additional information, Texas A&M AgriLife Extension Service has a field guide at https://insects.tamu.edu/fieldguide/aimg82.html .

When young cicada nymphs hatch from their eggs, they dig themselves into the ground to suck the liquids of plant roots. They spend several early life stages in these underground burrows before surfacing as adults. The process varies in length but often takes a number of years. Periodical cicadas do not create destructive plagues, as some locusts do, though tens or hundreds of thousands of insects may crowd into a single acre. Large swarms can overwhelm and damage young trees by feeding and laying eggs, but older trees usually escape without serious damage.

Do you think nature should be part of our everyday life, not just somewhere to go on the weekends?  You are invited to attend our free, open-to-the-public, monthly program every fourth Monday at 7 pm at the Red Oak Library, 200 Lakeview Pkwy, Red Oak, TX.  For more information on the Indian Trail Master Naturalist Chapter, contact the Texas A&M AgriLife Extension Service at 972-825-5175 or visit our website: https://txmn.org/indiantrail/ .

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