Kritsky of Mount St. Joseph has found that April temperatures guide the cicadas' emergence schedule.
He studied historical emergences and found accurate records for four different appearances dating back to 1885.
"Average April temperatures had a good correlation with emergence—which means temperature increases impact the emergence date," Kritsky said.
Based on April temperature records, Kritsky created a formula that predicts when a brood will appear. So far he has had extremely good results—he nailed the May 14, 2004, emergence of Brood X in Cincinnati and the first appearances of this year's Brood XIII in Chicago.
Kritsky said that he wasn't surprised by this year's early Midwest arrival.
Cicadas in a Warmer World
In the event of continuing climate change, the potential impacts to cicadas are unknown.
"If there is something like global warming, what are the direct consequences of that?" the Field Museum's Summers asked.
"One would expect our springs to come earlier."
If the point of optimal soil temperature when cicadas come out is moved up a month, "they will need to adapt or continue to emerge later on when it is much warmer," Summers added.
If a 65-degree-Fahrenheit (18-degree-Celsius) soil temperature is the key, "they may well emerge earlier," he said.
"The question is: How would they adapt to that? Would the trees [on which they depend] be different?"
Cicada broods have altered their cycles in the past, though it's unclear exactly why.
In Illinois in 1969, some of the insects came out after 13 years rather than 17 years, Summers said, only to return to the 17-year cycle.
Scientists have assumed the switch to a 13-year cycle had something to do with the climate, Summers said.
"It could have been an extremely cold winter, an extremely hot summer—we really don't know," he said. "We don't have enough people out there tracking this."
There will be plenty of golden opportunities to learn more. Although Brood XIII will be history by July, leaving millions of corpses behind, another swarm is imminent.
Next summer, the mid-Atlantic and Midwest regions will brace for Brood XIV.
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