According to the Indy Star, Brood X, a periodical cicada that emerges every 17 years in certain parts of the country, would be "a natural phenomena you won't miss. Cicadas will be everywhere - on your lawn, in your trees, and possibly even on you - and they are noisy." But in recent weeks, as cicadas emerged in Washington D.C., Cincinnati, and parts of southern Indiana, it seemed that many Indianapolis residents did, in fact, miss this phenomenon.
I surveyed users of Reddit.com who live in Indiana, and the results suggest that most Indy residents have not seen a single cicada near their home this year. Most of these people expected to see cicadas, and many of them describe their reaction to this year's periodical brood as "disappointed." So what happened? Are the cicadas dying out, or is their geographic range changing? Did someone invent the idea of cicadas swarming Indianapolis, somehow convincing Indy residents that this was actually a thing that happens every 17 years?
Survey results
There were 93 responses to the survey with usable location data within the state of Indiana. Of 13 Hoosiers located north of the Indianapolis area (Marion County plus neighboring counties), none reported seeing a single cicada. Of the 14 to the south of the city, 71 percent reported seeing cicadas. In the Indy area, just 11 of 66 respondents (17 percent) saw a single cicada this year.
A closer look at the geography of reported cicada sightings shows that most of the sightings in the Indy area were in the northeast part of the city near the Geist reservior and Fort Harrison State Park, as well as a couple in the suburbs of Carmel and Fishers. While this probably confirms the presence of some Brood X cicadas in Indianapolis, it doesn't quite live up to the predictions of a cicada invasion of the sort many experienced in Washington D.C.
This is confirmed in responses to the survey that indicate that 86 percent of Indy residents (and 100 percent of Hoosiers north of Indy) saw fewer cicadas than they expected to see. In constrast, only half of Hoosiers living south of Indy saw fewer cicadas than expected, and over a third actually saw more than they expected to see.
The two dominant sentiments expressed by respondents in Indianapolis and to its north were disappointment and relief, suggesting that many had been excited about the predicted cicada swarm, while others had been less enthusiastic. South of Indy, the most common reactions were positive, with a minority expressing disgust or disappointment.
What influenced people's expectations of Brood X in 2021? Since the brood emerges every 17 years, one might expect that in areas where Brood X was prevalent, long-time residents would based their expectations on memories of the previous invasions. Only 42 percent of Indy residents indicate that their own experiences influenced their expectations for the 2021 emergence, compared to 79 percent of residents of southern Indiana. Basing expectations on news media and other sources was much more common in Indianapolis (74 percent) and northern Indiana (77 percent) than in sourthern Indiana (50 percent). This suggests that where personal and community experiences with Brood X cicadas were less common, the news media might have filled in the gap, raising expectations where cicadas were not actually common in recent history.
News coverage of Brood X
Various news outlets reported on Brood X cicadas this spring, and many published maps of the brood's range. Several of these outlets used maps based on county-level data from the U.S. Forest Service, including the Washington Post, New York Times, Indy Star, CBS News, PBS, Vox and USA Today. On the surface, there's not much reason to doubt this data. It comes from an official source and it seems to be based on previous research. But the data it uses is actually somewhat old, and not very reliable for predicting cicada geography today. It is based largely on the work of late 19th century entomologists, C.V. Riley and Charles Marlatt, recoded to match today's counties.
Newer research from University of Connecticut entomologist John R. Cooley, using modern technology for field mapping and crowd-sourcing, demonstrates that Marlatt's methods were not very precise and often led to overestimating the range of periodical cicadas. Combined with the fact that cicadas might have actually been more widely distributed a century ago than they are today, the data from the U.S. Forest Service does seem to overestimate today's Brood X range. Large portions of Indiana, Ohio and Pennsylvania are included in the U.S. Forest Service map, but do not appear in Cooley's data.
There do appear to be a couple reports of cicadas in northeast Marion County in 2004—consistent with the survey data showing a similar cluster in 2021—but the data generally does not indicate many cicadas in central Indiana or to its north.
Cooley and other cicada researchers are currently mapping the 2021 Brood X emergence, and crowd-sourced reports are again part of the strategy. You can download the Cicada Safari app to submit pictures or mating calls to have your reports verified and added to the Cicada Safari map. Perhaps with better data, we'll all have more realistic expectations for the next emergence in 2038.
