Earth riddled with holes in springtime is a sign of an impending cicada emergence.
Insect aficionados may have followed the hubbub surrounding the appearance of Brood XIX of the 13 year periodical cicadas this spring. Like the cicadapalooza we enjoyed in 2004, 2011 is the year cicadas emerged by the millions in a broad swath from Oklahoma to North Carolina. Four species that comprise brood XIX are Magicicada tredecim, Magicicada tredecassini, Magicicada tredecula, and a newly discovered species named Magicicada neotredecim.
As a cicada lover, I was more than a little jealous of our neighbors in southern and central states that were able to witness this phantasmagorical event. Fortunately, a couple of weeks ago, I began hearing reports of cicadas emerging in St. Mary’s county here in Maryland. These reports were confirmed last week when intriguing images of periodical cicadas arrived in my email. Upon closer examination of the distribution map of Brood XIX (click here to see distribution), one remarkable location was as an outlier to the other populations of the great southern brood, a tiny speck in St. Mary’s county in Maryland. One major concern and oft discussed aspect of periodical cicada lore is their declining range. During the history of human occupation of North America, several localized broods of cicadas have disappeared, gone extinct. In his classic treatise on the biology and ecology of periodical cicadas, C. L. Marlatt mentioned the disappearance and shrinking distributions of several cicada broods in the United States. Experts suggest that fragmentation and elimination of cicada habitat due to farming and urbanization may be linked to vanishing cicadas in some locations.
Shed cicada skins, called exuviae, decorate trees and shrubs.
So, to witness this brood of magnificent creatures that may someday wink out of existence in Maryland, I loaded up my car with camera gear and set off in search of Maryland’s Brood XIX - the St. Mary’s survivors. After a disappointing search that consumed most of one day and yielded a single sighting, I was richly rewarded two days later with the otherworldly songs of thousands of cicadas in treetops festooned with egg-laying females and courting males near the small hamlet of Dameron in southern St. Mary’s county.
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 thirteen years only to perish attempting to molt or while trying to reach the safety of the trees.
Singing the right song seemed to pay off for this happy guy.
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 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. Cicada nymphs 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. Cicadas have survived in North America for millions of years. Early records of cicadas date back to colonial times. A report from the April 3, 1751 edition of the Maryland Gazette noted that “We are informed from many Places, that the Caterpillars appear already in vast numbers, and in some Places the Locusts have been found in great plenty, just under the surface of the Earth, almost at their full growth: May God avert our impending Calamities.” Well, we all know that locusts are not really found “just under the surface of the earth,” but in April cicadas ready to emerge would be found in droves. If you do the math, it is most likely that the locusts in this report were really the fully developed nymphs of Brood XIX cicadas ready to make their appearance. How marvelous! So, let’s hope that 2011 is another successful season for St. Mary’s survivors and that in 260 years, after another 20 broods, these wonders of nature will still be with us.
References
Bug of the week thanks Gail, Paula, and Christian for wrangling and hunting cicadas, and serving as the inspiration for this episode. The marvelous references “The periodical cicada” by C. L. Marlatt and “Reproductive character displacement and speciation in periodical cicadas, with description of a new species, 13-year Magicicada neotredecim” by D. C. Marshall and J. R. Cooley were used to prepare this episode.
To learn more about these really cool insects, please visit the following web sites:
http://insects.ummz.lsa.umich.edu/fauna/michigan_cicadas/periodical/Index.html