Three years ago the east coast was visited by billions of red-eyed bugs called Brood X periodical cicadas. Many people thought that like some strange biological equivalent of Haley’s comet, these boisterous bugs returned only once every seventeen years. This was a source of despair for those that loved them and a source of relief for those that didn’t. Male cicadas vibrate a small drum-like organ called a tymbal found beneath their wings to produce a variety of calls. Part of the story not known to all was that in other parts of the country other broods of cicadas are found in intervening years. Imagine my delight to know that 2007 is the year to visit the windy city to witness and enjoy Brood XIII cicadas. Last week I spent several days in Elmhurst, a delightful suburb of Chicago. Elmhurst turned out to be cicada central for Brood XIII.
After seventeen years sucking sap from roots of trees underground, cicada nymphs emerged by the millions just in time to shed their skins and fly to the treetops to serenade marching bands and veterans in Elmhurst’s Memorial Day parade. The life of a cicada is mysterious and precarious. When their development is nearly complete in spring, they construct an escape tunnel to the surface of the earth. Soil temperatures in the middle sixties seem to be a cue that the world above ground is warm enough to support flight and reproduction. Many nymphs emerge at night and make a mad dash for vertical structures such as trees and shrubs, however lampposts, street signs, and slowly moving people seem to work just as well.
After climbing up and away from the soil, they attach to a firm object to begin the process of molting. Their outer skin, or exoskeleton, splits along a predetermined line on their back and the beautiful adult cicada wiggles free from the shell. The freshly molted adult is almost pure white except for bright red eyes and patches of black behind the head. Before its skin hardens, the cicada must expand its wings or it will be unable to fly and seek a mate. After wings and legs have hardened, cicadas scurry or fly to the treetops. Emergence from the earth and the final molt are perilous times for cicadas. Many cicadas survive interment underground for seventeen years only to perish attempting to molt or to reach the safety of the trees.
Male cicadas have evolved a unique structure called a tymbal. These paired organs are located on the sides of their bodies just beneath the wings. The tymbal is vibrated much like a drumhead to produce sound. Males produce a variety of calls for different purposes. If threatened by a predator such as a bird or a squirrel, a loud squawking noise is made in an attempt to startle the predator and make an escape. The principal function of the tymbal is to produce calls that assist in finding a mate and winning her affection. One type of call attracts both males and females to a common assembly place such as a large tree. When guys and gals get eye to eye, the male will use three distinct and different courtship songs to try and convince the gal that he should be the father of her nymphs. If the lady likes his advances, she will signal her approval by flicking her wings with an audible click.
After mating, the female cicada will move to tender young branches to lay eggs. Using a saber-like structure on her abdomen called an ovipositor, the female gouges groves into the woody tissue and lays 20 to 30 eggs in an egg nest. This process is repeated on one or more plants. Females lay as many as 600 eggs. After incubating for more than a month, eggs hatch and tiny nymphs a few millimeters long dive to the earth beneath the tree. In a matter of minutes, they burrow into the soil, find roots, and insert a small straw-like proboscis into the roots. The cicada nymphs then hunker down underground, sipping sap and slowly growing larger.
Despite what you might have heard, cicadas are not blind. Their red eyes see fine. They do not bite, although, if very thirsty, one may probe you a bit with its tiny beak in search of moisture. Periodical cicadas are not one species. Three species of 17 year cicadas and four species of 13 year cicadas are known. Seventeen year cicadas occur in 12 broods and 13 year cicadas are found in three broods occurring primarily in southern states. Many mysteries remain concerning their evolution, distribution, and synchronous appearance. Without a doubt, they are a true marvel of nature and one that should be enjoyed whenever possible.
This week I give special thanks to Mark Hanner and the gang at CBS for providing an opportunity to visit Brood XIII. To learn more about periodical cicadas and cicadas in general, please visit the following excellent web sites.
To see my recent visit with some Chicago style cicadas, please click on the following link.http://www.cbsnews.com/stories/2007/05/29/eveningnews/main2864905.shtml