We were traveling south on Interstate 65 just outside Nashville, Tennessee -- my wife driving too fast as usual -- when suddenly our car was pelted with what seemed at first like bullets. No car was near enough to lift stones off the road and clear skies eliminated hail as another possible culprit. Most of the objects ricocheted off the front of the car but finally when several squished against the windshield we knew that we were driving through an insect swarm.
Doris pulled onto the median and we got out, hesitantly, to see if we could find and identify the bugs.
Finding them was easy -- they were everywhere. The air was full of them buzzing about and thousands crawled on the ground. Injured or dead bugs littered the highway and the shoulders held even more, swept there by air currents around speeding traffic.
We captured a few in my ever-ready glass jar to examine more closely. It was immediately apparent that they were cicadas, their translucent veined wings held roof-like over heavy black bodies. They had bright orange compound eyes and more orange marked their backs and spread into their wings.
We had chanced upon an outbreak of periodical cicadas -- what many people call 17-year locusts. There are problems with that popular designation. Cicadas are not locusts: locusts are related to grasshoppers and crickets while cicadas belong to the same family of true bugs as aphids and leafhoppers. And these southern cicadas have a 13 year life cycle.
All cicadas -- our dog-day cicadas on the Niagara Frontier included -- have multiple year life cycles, spending from 4 to 17 years as nymphs underground before burrowing out to enjoy their few weeks as adults, but some fraction of the population of most species, again including ours, matures each year. Only these 13-year and the generally more northern 17-year cicadas of the genus Magicicada have these widely spaced outbreaks and are called periodical.
Entomologists have identified the emergence years and ranges of these unusual bugs. Somewhere in the eastern United States a brood of 17-year cicadas emerges in 12 of those 17 years but 13-year cicadas appear in only 3. Simple arithmetic (13 times 17) indicates that the two periods occur again in the same area only after 221 years and in a few counties in western Missouri and southeastern Oklahoma 1998 is one of those years. They not only have these 13-year cicadas that we were seeing in Tennessee but 17-year cicadas as well. They must be overwhelmed.
We don't have periodical cicadas here on the Niagara Frontier but just east of us through the Finger Lakes region a 17-year brood will emerge in 2001.
I am intimidated by the large size of these bugs but they don't bite or sting. (The female's stinger-like ovipositor is only used to deposit her 400 eggs.)
Shortly after we resumed our drive south I felt something unusual and slapped it off the back of my neck. The immediate response was a car-filling screech. Thank goodness I wasn't driving as I'd have had us in the ditch. With much effort my wife maintained her composure, realizing that a cicada had joined us. Now lost among our luggage it "entertained" us for the rest of our trip with occasional alarm clock screams.
Cicada egg laying often kills twigs which represents a problem for fruit growers, but otherwise the damage they do is minimal. Of course their predators -- birds, animals and other insects -- grow fat on the juicy bugs. The cicadas' brief appearance in such huge numbers serves as a kind of defense against this, their enemies able to devour only a fraction of the population in such a short time, and the remaining females deposit plenty of eggs to produce another brood.
Although we never saw as many again, these periodical cicadas were part of the background everywhere we went in Tennessee and Alabama.
Much technical information for this column was obtained from the outstanding
web site maintained by John Cooley, David Marshall and Mark O'Brien for
the University of Michigan Museum of Zoology Insect Division. Of special
use to serious entomologists are their accompanying bibliographies. Another
excellent site with many illustrations and further links is Dan Century's
Cicada Mania. The
included with this column is copied with his permission from Dan's
own photograph of a Magicicada species at that site. Finally, a
site that I
did not find until after this column was prepared that gives a great deal
of detailed information about the species we met in Tennessee and Alabama
Cicadas ("The 13-Year Locusts") in Alabama, maintained by Auburn
University entomologist L. L. Hyche. How lucky we amateurs are to
have this kind of information shared by professionals of the highest