Cicadas East, Cicadas West

by Carl Strang

Today’s puzzle is the odd range boundaries of two cicada species that occur in the 22-county area I define as the Chicago region.

The scissor-grinder cicada (Neotibicen pruinosa) is one of the four most abundant annually-appearing cicadas in northeastern Illinois.

Scissor-grinder cicada

Though individuals may sing occasionally from mid-morning to dark, their ee-oo-ee-oo-ee songs especially dominate the wild soundscape at dusk in mid- to late summer. In the following recording, the cicada is introduced and ushered out by a nearby striped ground cricket.

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A recent review of North American cicadas (Sanborn and Phillips 2013, Diversity 5: 166-239) shows what appears to be a gap in the species’ distribution in north central Indiana. I was inclined to regard this as simply indicating a lack of sampling in that area, but this year I pushed to complete my own map for scissor-grinders. Here is the result:

Black dots indicate counties where I have observed scissor-grinder cicadas.

The numbers of scissor-grinders thin out dramatically in the eastern and northern counties of the region. I cannot find them at all in Walworth, Berrien, St. Joseph or Fulton Counties. They barely reach the southwest corner of Marshall County. Sanborn and Phillips show them picking up again farther east, but only one record each for Wisconsin and Michigan, in both cases outside my region.

There is no obvious explanation for the Indiana gap. It does not correspond to soil type, as scissor-grinders can be found in both sand and clay soil areas, and are absent from areas of both.

Swamp cicadas (N. tibicen) have a distribution mainly south and east of the Chicago region, and Sanborn and Phillips (2013) do not map them into the Illinois or Wisconsin portions of my region. My work extends that range a little, but they are scattered individuals in Illinois, with only one Kane County and one Kankakee County site.

Swamp cicada

Black dots indicate counties where I have observed swamp cicadas. Red stars show locations of the northernmost records.

Their song is a percussive vibrato. Here is a recording from southern Indiana in which several individuals provide overlapping songs:

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They occur mainly in the Kankakee and DuPage River areas in Illinois. In the southeastern portion of the region, a few can be found along the Tippecanoe River in Fulton County, but they apparently drop out before that river reaches Pulaski County, which also is well south of the Kankakee River drainage. The swamp cicada’s range boundary is a western one, but explaining it is just as difficult as in the scissor-grinder. St. Joseph County seems to be the center of abundance in the region, with Potato Creek State Park having an especially high density.

The practice of science is largely about questions, and these newly discovered odd range boundaries provide good ones for these two cicada species.

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1 Comment

  1. August 19, 2018 at 4:16 pm

    That’s really interesting. There is a sizable gap in Ohio for Scissor-grinders, and Cleveland is right in that gap. (Too bad for me, as I really love them!) They are abundant in western Ohio along the lake shore counties and they are also in southeastern Ohio.

    Interesting, too, about Swamp Cicadas. I haven’t encountered a gap here.

    I truly love the careful detail of your work and what you discover as a result!


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