Septendecim Surprise

by Carl Strang

A year ago I was busy in June documenting a 4-year-early emergence of periodical cicadas in a part of northeast Illinois. Periodical cicadas come out in large numbers somewhere in eastern North America each year, and the different areas and years are called “broods,” designated by Roman numerals. The northeast Illinois ones are in Brood XIII and their next main emergence will be in 2024.

This is the year for Brood X, which occupies a large portion of the eastern U.S. According to Gene Kritsky, who has thoroughly researched the history of these insects, Brood X periodical cicadas at one time emerged in every Indiana county. Now they are known mainly in the southern half of that state, but it seemed appropriate for me to check the 10 northwest Indiana counties of my singing insects study region for possible survivors. I didn’t expect to find any, as none have been reported there in recent years.

My own research has shown that forest size matters to these insects, so I used GoogleEarth to pre-select the largest forest blocks to visit in each county. I began in my childhood home county of Marshall and found no cicadas, either in forests on sandy soils or on the glacial moraine east of Lake Maxinkuckee.

I proceeded to Fulton County, just south of Marshall. I stopped beside County Road 450N east of US31, turned off the car motor, and listened. Could it be? Yes, I was hearing a chorus of “pharaoh,” the calling song of Linnaeus’s 17-year cicadas, Magicicada septendecim. I made a recording and continued down the road. I was gratified to find an entrance to Richland Restoration Park, which had trails into the forest. Newly emerged cicadas were resting on vegetation beside the trail.

The orange line between eye and wing separates septendecim from the other 17-year cicada species.

Shrubs with the cicadas were frequent along the trail.

Though one little area of 3-4 square meters had 25 cicadas, much of the way along the trail had none.

My overall impression was that these cicadas still were short of their peak, and I intend to return. I want to get some idea of how big this population is, how extensively it covers its forest, and whether any of the other 17-year cicada species also will emerge. Without the frequently more numerous Cassin’s 17-year cicadas (M. cassinii) to buffer them from predators, can the septendecim persist? In any case, I was pleased to find that at least one genuine Brood X remnant hangs on in my region. I still have a few more counties to search.

As the county road designation indicates, the park is 4.5 miles north of Rochester. It is closed on Wednesdays and the second Saturday of each month. The cicadas will be done before the end of June.

3 Comments

  1. James C. Trager said,

    June 7, 2021 at 2:33 pm

    I’ve seen a few cast skins and heard an adult Magicicada or two here 35 miles west of St. Louis this last week. I don’t know if these are off-year Great Southern Brood or ???

    • Susan C. said,

      June 7, 2021 at 6:05 pm

      I find their life cycles deeply confusing, but always fascinating.

    • natureinquiries said,

      June 8, 2021 at 6:52 am

      The specialists who pursue these cicadas each year now emphasize quantifying observations. Stragglers like you describe can be confusing, as you suggest. They are not disregarded but are de-emphasized in understanding the overall patterns. Early records did not make that distinction, emphasizing presence or absence, hence the need for clarification.


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