Cicada Search Concluded

by Carl Strang

A week after my first visit I returned to the forest in Fulton County, Indiana, that had begun to show a significant emergence of periodical cicadas described in the previous post. I found them well into the peak of their appearance. There were more newly emerged cicadas than before, and fresh cicadas and emptied nymphal skins were visible all along the trail in the forest interior.

This time, skins outnumbered new cicadas. The only species present remained Linnaeus’s 17-year cicada, Magicicada septendecim.

The chorus was very loud, and as I drove the nearby roads to determine the extent of this emergence, I found that I could hear it clearly from a quarter mile away and it was audible from half a mile. It extended a mile north of the road where I first encountered the cicadas, and was as much as half a mile wide, but there are clearings within that block so that the forest with cicadas covers an estimated 243 acres or 98 hectares, which my earlier research suggests should be plenty large enough to sustain this population.

Between the two visits, and after the second one, I checked the remaining large forest areas in the 10 counties of northwest Indiana. I found nothing comparable to the Fulton County emergence. There were a few scattered (countable) septendecim in a portion of Potato Creek State Park in St. Joseph County, and the same in a small area of the Kingsbury Fish & Wildlife Area in LaPorte County. Beyond those there were only a few singles, two septendecim in LaPorte County, two Cassin’s 17-year cicadas (M. cassinii) in Porter County, and one cassinii in Lake County.

Considering these observations and historical records, I suspect that the Kankakee River and its broad sandy soil region represents a dividing line between Broods X and XIII in Indiana, at least in the western part. Brood XIII then would extend eastward along the elevated Valparaiso Moraine between the Kankakee River and Lake Michigan. If so, that would place the Fulton and St. Joseph County cicadas in Brood X. The singles in Lake and Porter Counties would be stragglers of Brood XIII. The LaPorte County septendecim may represent vanishing traces of Brood X that once spilled onto the Valparaiso Moraine from the east.

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