Periodical Cicada Tunnels

by Carl Strang

On Monday I went to Wood Dale Grove and Salt Creek Park Forest Preserves in DuPage County and looked for periodical cicada tunnels. As mentioned in the previous post, these are dug to the surface by nymphs, often weeks before they emerge to molt into their adult form.

My choice of those two preserves was not random. In the 2007 major emergence there were practically no periodical cicadas in the adjacent cities of Addison and Wood Dale, but residents reported that there were plenty in 2003. I had found no cicadas in either of those preserves when I checked them in 2007. Is it possible that those cicadas had completely shifted their timing to form a separate population? If so, this would be scientifically significant. I started finding cicada tunnels soon after entering the forest at Wood Dale Grove on Monday. I was elated at what I saw when I lifted a piece of old concrete.

Three cicada tunnels were in that one small area.

In 40 minutes of searching I found 10 tunnels. A couple were in chimneys, similar to those some crayfish produce.

Cicada chimney

How did I know these were not crayfish tunnels? Size tells the tale. A periodical cicada tunnel is half an inch in diameter, around the size of my forefinger. Crayfish tunnels are at least as big around as a quarter. Nightcrawler tunnels are much smaller, less than a pencil’s diameter.

Most of the tunnels I saw were sheltered, like those under the concrete, under bark or an overhanging fallen tree stem. Those in unsheltered bare soil had sharp edges, indicating they had been dug in the few days since a very heavy rainstorm passed through. Were it not for that storm, I believe I would have seen many more, as the rain washed soil into the tops of the tunnels.

At Salt Creek Park it was much the same story. In low areas resembling those at Wood Dale Grove I found tunnels at the same rate, one sharp-edged one about every four minutes. I did not find any in the upland woods, which may prove to be significant. Cassin’s 17-year cicadas are associated more with lowland woods, Linnaeus’s 17-year cicadas with uplands.

All of this has me very much looking forward to what I will find in a few weeks in this area. If there is indeed a major emergence in these two preserves, which are fairly close together, what is the extent of the emergence area? Are both species involved, or just the one? Can I document mating and egg laying? And, of course, all of this observing must be done under the social distancing, mask-wearing safety protocols dictated by the covid epidemic. Stay tuned.

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