“For the last several miles we’ve been hearing this terrible noise. We think the fan belt is slipping, but it’s a new truck, so…” Just then they heard the terrible noise again. But it wasn’t coming from the engine at all. It was coming from the mesquite tree above their heads!
“Oh, that noise!” I said. “That’s just a cicada calling. Don’t you have them in Austin?”
Apparently not. They said they’d never heard anything like it! I am sure they would have remembered such an ear-piercing whine!
This encounter piqued my interest. I thought cicadas were everywhere. I know sometimes they are erroneously called “locusts,” but even if you didn’t know the correct name, you would still recognize the sound. I mean, a cicada by another name would be just as loud!
After I checked several Internet sites, including those with sound files of cicadas calling, I discovered that we have a very special cicada here in South Texas. It is called the Giant Cicada (Quesada gigas). The Giant Cicada is actually a tropical cicada, and it is found from here south to Argentina.
In recent years, the Giant Cicada has been expanding its range northward. It now seems to occur fairly regularly in Bexar and Travis counties, although the distribution of the insect could be somewhat spotty. Some of us “old-timers” say that they have always been in the San Antonio and Austin areas. I am sure I remember them from my childhood in Central Texas. How could I ever forget such a sound?
The first time someone hears the Giant Cicada, he invariably tries to describe it in terms of some other loud sound. Henry Walter Bates in his book, The Naturalist on the River Amazons (1863), wrote that a cicada’s song ended “in a long and loud note resembling the steam-whistle of a locomotive.” Texans have described it as “the sound of summer” in places like Laredo. One fellow, on first hearing it, thought his mule was sick. A veteran said it reminded him of air raid sirens during World War II. Modern comments usually mention some sort of machine: a loose fan belt on a car, an electric drill, a jet engine. A few say that the sound might be made by a strange new bird.
One day, my cat came in the cat door with a cicada in his mouth. I didn’t see it at first but soon the bug let out its screaming whine. I was momentarily shocked by what I thought was the cat’s strange cry. It sounded like the cat was going to be sick! Or was possessed by aliens! I put the cat out.
My favorite comment was made by David Huffman, a biology professor at Texas State University in San Marcos. He said, “At first I thought it was someone working with a router.” That is, until he realized that the maniacal neighbor using the router (at all hours of day and night) had to be in the top of a tree!
Huffman was surprised by the appearance of Giant Cicadas in San Marcos. He has lived there for three decades and had never heard one until recently. Entomologists suggest that climate change may be allowing this species, along with others, to move slowly northward.
How can an insect, even a large one like the 2-inch long Giant Cicada, make such a loud sound? The amazing sound-producing organs are located on the abdomen of the male. There are two of these tymbals. Inside the organs are membranes edged with chitin. The insect uses special muscles to pull these membranes, producing a click or pop. This sound is somewhat like the pop you make when push down on a jar lid. He can make the pops in such rapid succession that they merge into a buzz or whine.
But the loudness comes from the resonance chamber inside his abdomen. Just before he calls, he sucks in air into an air sac, causing his abdomen to bulge. This large air-filled chamber is like the body of a guitar. It greatly amplifies the sound.
The loudness of a cicada’s call has been measured at between 100 to 120 decibels at close range. This is considered to be at the threshold of pain to human ears, if the insect is right at your ear. (I don’t think I would let one get that close!)
So how does the male cicada not damage his own ears when he calls? The cicada’s eardrums are on its chest, just a fraction of an inch away from its sound-producing tymbals. One theory is that the male cicada can disable its hearing organs while it is making the loud noise. This is interesting, if true. I wonder how he does it.
The whole point of the male cicada’s call is to attract the females to the treetops to mate. Once mated, a female will move down the tree to a small branch or twig and lay her eggs in the crevices of the bark. When the eggs hatch, the young fall down and bury themselves in the soil. At this stage, they resemble small wingless adults and are called nymphs. The nymphs feed on the roots of trees, especially legumes like huisache and guayillo, for up to five years. As they grow, they shed their skin five times. On the fifth molting of the exoskeleton, the nymph tunnels out of the ground and climbs up a nearby tree trunk. Clinging by its six legs, its back splits open and the winged adult emerges. The discarded exoskeleton remains attached to the tree.
The newly emerged adults fly off to start a new cycle of life and emit a new chorus of screaming, ear-piercing sound. Aren’t you glad you live in South Texas, where you can hear the calls of the Giant Cicada?