First Flags Over Brookfield

by Carl Strang

Cicada specialist John Cooley taught me a new term: flagging. This refers to dead and broken twig ends on trees and shrubs where periodical cicadas have placed their eggs. Mama cicada slits the underside of the twig in several places and injects her eggs. This impedes water flow, and with circulation cut off the leaves turn brown. The cuts weaken the twig, and it may break partly and bend down, producing a “flag.”

Now that the periodical cicadas are done singing in many places and nearly so in others, it is time to start looking for these flags. They will provide the best measure of how this off-year emergence may continue for another generation. On Tuesday I started in Brookfield, the first place where I heard a full wave chorus of singing males.

I soon found a tree with many flags.

This tree was in the same place where I found that initial wave chorus.

The brown, drooping flags stand out against the green foliage. This prunes the tree a bit but will not cause significant harm. I saw many trees with one or two flags, but only the two in the photos had many. I expect to see more of them the next time I check.

John said that dry weather and thunderstorms enhance flag formation. A lack of water flow enhances the twig-end drying, and the buffeting winds of storms partially snap the weakened twigs. I heard no singing cicadas in Brookfield, and so this is the very beginning of this process. On the way home I swung through northern Hinsdale, another area that had abundant wave chorusing at the peak. There still were many small non-wave choruses, so it was not surprising that I saw only a couple flags during the drive-through. I am hopeful that flagging will develop over a period of weeks, allowing me the time needed to get a good assessment of periodical cicada reproductive success across the Chicago area this year.

No Shadow of a Shadow

by Carl Strang

I didn’t find any periodical cicadas out in Addison or Wood Dale this year. That might seem like a strange statement, given that our local main emergence last happened in 2007, and the next is due in 2024.

A 2007 photo of representatives of DuPage County’s two species of 17-year periodical cicadas: Linnaeus’s on the left, Cassin’s on the right.

A 2007 photo of representatives of DuPage County’s two species of 17-year periodical cicadas: Linnaeus’s on the left, Cassin’s on the right.

I had reason to think I might find a few of these amazing critters here this year (they are peaking in Ohio in 2016, by the way). For several generations, now, starting in 1969, significant numbers of the cicadas have emerged 4 years early in the western suburbs of Chicago. This phenomenon, called a shadow brood, since has been found in a few other locations in eastern North America. It generally is thought to be a one-time deal, but the repetitive nature of this local shadow brood has me thinking there has been reproduction each time. Furthermore, the cicadas in the adjacent cities of Addison and Wood Dale appear entirely to have switched to the shadow timing. Residents reported them to be abundant in 2003. I found hardly any there in 2007.

The next shadow brood emergence therefore should happen in 2020. That assumes that there was indeed reproduction in 2003, or at least that local conditions again will result in some cicadas emerging at age 13 rather than 17. Those numbers are significant, as southern broods of related cicada species always are 13-year cicadas. Something caused a switch in some of our cicadas, in 1969 at least, bumping them onto the 13-year track. If they have been reproducing, then the subsequent shadow broods have resumed the 17-year life span. If you have followed this convoluted story, then you can guess why I thought I might find a few periodical cicadas this year. If the shadow brood indeed is all that exists now in Addison and Wood Dale, and something were to cause a few of them to make the 13-year jump now, 2016 is when they would have emerged. Perhaps a few did, but if so I did not hear any singing, nor did I see any shed nymphal exoskeletons, in this year’s tour of the two cities.

I will repeat my route each year, as I have done starting in 2014. A few cicadas out of the millions emerge a year or two early. I will be very surprised if there are any next year, but the anticipation will build as I look to a possible major emergence in Addison and Wood Dale in 2020.


A New Periodical Cicada Puzzle

by Carl Strang

I have been getting questions from people asking about periodical cicadas this year. They have been hearing reports of brood XIX, the simultaneous emergence of several species of 13-year cicadas to the south of our area. I have been giving the sensible answer that no, we won’t be getting them in northeast Illinois. That was up until Tuesday afternoon, when I heard three periodical cicadas singing on the Mayslake Forest Preserve mansion grounds.

The songs were those of Cassin’s periodical cicada. This is a photo from the 2007 main emergence in our area. The insect on the right is a Cassin’s 17-year cicada, the one on the left is our other local species, Linnaeus’ 17-year cicada.

But that wasn’t all. That same day I heard another singing cicada half a county away from Mayslake, at forest preserve district headquarters. Then yesterday I heard individuals at two more locations on the Mayslake preserve, and two in west central DuPage County, where there were very few scattered individuals in 2007. Furthermore, I have heard reliable reports of singing periodical cicadas in other DuPage County locations.

I don’t see any way to connect this to the 2007 emergence. True, a few late cicadas came out in 2008 (I called them Oops Cicadas), but that is to be expected. There were none in 2009 or 2010. The question I would like to have answered first is whether these are 13-year or 17-year cicadas. There is a 13-year species with the same song as cassini. I hope I can get specimens, a shed nymphal exoskeleton at least. That could be held for potential future DNA checking. This would establish whether these might be outliers of brood XIX. The thing is, most people don’t listen for singing insects. We don’t really know what is going on with periodical cicadas outside of peak emergence years or core emergence areas. If I learn anything new, I’ll pass it on, but I will try to get as many location observations as I can in the limited time I have to devote to this unexpected development.

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