Geography of Periodical Cicadas (Hemiptera: Cicadidae) in Portions of Northeast Illinois and Northwest Indiana

Brood XIII periodical cicadas (Magicicada Davis) in DuPage County, Illinois, emerged in 2024 in an area that extended as much as 10.6 km beyond the edge of the previous main emergence in 2007. The implied dispersal of gravid females is greater than has been reported elsewhere and may reflect adaptation to a historical landscape of scattered wooded islands within a matrix of prairie. A series of four-year-early emergences in northeast Illinois, first described in print in 1969 and subsequently occurring prior to each succeeding main emergence, was quantified for the first time in 2020. The largest densities of singing males were observed in residential communities adjacent to the first two railways connecting Chicago to its suburbs, where pre-settlement prairie first had been replaced by urban forests. The 2020 emergence did not include pre-settlement forests. In surveyed communities, reproduction in 2020 measured 7.9% of that in the main Brood XIII emergence. There is an indication that significant reproduction also occurred in 2003. Several possible explanations have been proposed, but the primary driver of these early emergences remains to be determined. Three populations of Brood X cicadas persist in northwest Indiana, with the Valparaiso Moraine being the likely landscape feature dividing Broods X and XIII. The Magicicada species in northeast Illinois and northwest Indiana belong to two species, M. cassini Fisher and M. septendecim L. To date there is no documentation of M. septendecula Alexander and Moore, a third species of 17-year cicada known in other brood areas.