Periodical Cicada Behavior

by Carl Strang


This post will conclude my account of periodical cicadas in DuPage County, Illinois, during the 2007 emergence. I had read as much as I could find, from the scientific and popular literature, regarding these insects, but there is no substitute for direct experience. It’s one thing to read that the choruses of singing males are loud, it’s quite another to find that you have to wear ear plugs during lunch time excursions because of concern that hearing damage might result from walking under chorus trees.




With that caveat, of course the literature described things well enough, for the most part. There are no absolutes, though, when you are talking about millions of individuals of any animal. Yes, they mainly came out at night. But some came out during the day, especially on rainy days. There were appalling numbers that became stuck and did not complete their emergence. These died half out of their nymphal skins, or sometimes simply had deformed wings and could not fly. I saw crinkle-winged females laying eggs, though. With numbers so great, finding a mate was easy, and so there appeared to be less selection against developmental deformities than you might expect.


Crinkle-winged female laying eggs

Crinkle-winged female laying eggs





I went out a few nights to observe emergence. On one cool night I heard rustling in the leaves on the ground, but nothing happened, and things quieted down. On a warmer night, the rustling proceeded to hordes of nymphs climbing plants to complete development to their final adult form.




The cicadas usually were quiet through the night and into the next morning, most flying into the tree canopies by mid-day following their emergence. I’m really just sketching here, there is so much that has to be observed first hand. Let me jump ahead to the most unexpected behavior of all.


The cicadas had been out for a couple weeks, perhaps, and had proved to be conservative in their movements. I found that, at the edges of main emergence areas, I could find choruses of males singing 100-200 meters farther out. They flew around some, but did not fly into the open.


Then suddenly, over a period of three days or so, all of this changed radically. Cicadas were flying out into the open, across wide highway corridors for example. After that brief period, small choruses of males were singing all over the county, even in areas where there had been no emergence. I found females in some of those places, too.


Emergence holes

Emergence holes





This was unexpected, and exciting. I didn’t recall seeing anything about this in the literature. So, what does it mean? Is this something that always happens? If so, it doesn’t mean much in terms of cicada populations. These adventurers will have no long term impact if they leave no descendents. But what if this was a unique event, brought about by some fortunate confluence of environmental conditions with a population that had reached a cusp from which large-scale expansion suddenly was possible? If the latter is true, there will be a radical change between the 2007 map and what will be observed in 2024. But, sigh, all we can do now is wait. The next generation is under ground, now, entering its 4-year dormancy at this point, continuing its slow count of years until the time is right for the next round of inquiries into the mysteries of the periodical cicada emergence in northeastern Illinois.

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