Some Cicada Site Maps

by Carl Strang

Today I close this series of posts on my site mapping project. Three of our Chicago region cicadas’ maps revealed interesting patterns that raised questions for me. Let’s start with the green-winged cicada (Diceroprocta vitripennis).

Green-winged cicada

Green-winged cicada all sites map

This is a species that is limited to sand soil areas along the edge of Lake Michigan and the Kankakee River. I was a little surprised that the latter sites all were south of the river, but that could be in part because I haven’t visited many sites on the north side. Now let’s consider another sand-soil species, the northern dusk-singing cicada (Neotibicen auletes).

Northern dusk-singing cicada, museum specimen

Northern dusk-singing cicada all sites map

What strikes me here is that the northern dusk-singing cicada extends much farther into the sandy southeastern counties. I’m a bit puzzled by this, as there is habitat in southeastern Starke County and southwestern Marshall County which seems very similar to places where I have found green-winged cicadas farther west. The only possibility I have come up with so far is that the green-winged cicada is smaller and weaker, and may not be able to find mates as readily in the fringes of its range.

A final case study, and the one that intrigues me most of all, is that of the swamp cicada (Neotibicen tibicen).

Swamp cicada

Swamp cicada all sites map

There are plenty of sites with swamp cicadas in the eastern two ranks of Indiana counties plus Berrien County, Michigan. That connects them to Cleveland, where Lisa Rainsong reports this as one of the most abundant cicadas. I had not realized, until I made this map, that I have found them only adjacent to the Kankakee River farther west in Indiana, plus the Momence Wetlands site in eastern Kankakee County, Illinois. I have spent plenty of time along that river farther west and have made no further observations. But then swamp cicadas show up again as scattered individuals and small groups in DuPage County and parts of the adjacent counties. For now I have to regard this as a disjunct part of the species’ range. Perhaps a few wandering individuals occasionally provide gene flow into this isolated northwestern group, but otherwise I wonder how long it has been separate in this way.

Site Map Fuzzy Boundaries

by Carl Strang

In the previous post I described my winter project of creating new maps showing all the sites where I have found each singing insect species in the Chicago region. A few of these produced surprises. Take the Texas bush katydid (Scudderia texensis), for instance.

Texas bush katydid

The all-sites map for Texas bush katydids.

The proportion of sites where I have observed this species is noticeably higher west of the Indiana border. Texas bush katydids occur through much of the eastern U.S., but they seem to thin out significantly in the eastern part of this region. I had no idea until I finished this map.

A similar surprise awaited in the maps for long-tailed meadow katydids (Conocephalus attenuatus) and black-sided meadow katydids (C. nigropleurum), two small wetland species.

Long-tailed meadow katydid

Black-sided meadow katydid, one of our most colorful singing insects

The all-sites map for long-tailed meadow katydids.

The all-sites map for black-sided meadow katydids.

As you can see, these are two species I don’t run into very often. What intrigues me is that I have found both only in the northern part of the region. Historically, at least, their ranges have extended well into southern Indiana, but is that still the case? Might these be examples of species losing the southern part of their ranges to climate change? This is one question I don’t think I have enough lifetime left to pursue myself, but perhaps others will be able to show that these species still are around farther south.

A final case for today is that of the tinkling ground cricket (Allonemobius tinnulus).

Tinkling ground cricket. Reddish tones distinguish this woodland-edge species.

Tinkling ground cricket all sites map

Here the map doesn’t tell the whole story. The sites in Indiana and the more southern Illinois counties have lots of tinkling ground crickets. The Cook, Kane and DuPage County sites represent observations of single individuals or, at most, fewer than ten. This seems to point to a drastic thinning northward, and makes the Lake County (Illinois) and Walworth County (Wisconsin) observations seem suspect. But going back to my field notes, I find that the Illinois Beach State Park and Lulu Lake Nature Preserve observations were of large, if isolated populations. What may distinguish them is the sand soil at Illinois Beach and similar gravelly soil at Lulu Lake. In DuPage, Kane and that part of Cook County the soils are clay based. So why haven’t I found tinkling ground crickets on the sandy soils of municipal parks in Wisconsin’s Racine and Kenosha Counties? Scientists love mysteries.

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