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In 2024, a remarkable natural event will unfold as two distinct cicada broods, one on a 13-year cycle and the other on a 17-year cycle, will emerge simultaneously for the first time in over two centuries. This synchronicity, last witnessed in 1803, will see billions of these buzzing insects emerge in the Midwest and Southeast for a loud and lively mating season.

This year’s concurrent emergence of Brood XIII and Brood XIX is an exceptional occurrence. Although it’s possible for a 13-year and a 17-year brood to emerge concurrently, each specific pairing aligns their cycles just once every 221 years. This year, the geographic territories of these two broods intersect, particularly in central Illinois, making the event even more unique.

“Considering Thomas Jefferson was the president the last time these two broods surfaced together, this is undoubtedly a rare event,” noted Gene Kritsky, an entomologist at Mount St. Joseph University in Cincinnati. Kritsky, who penned “A Tale of Two Broods” about this phenomenon, highlights the rarity and significance of this dual emergence.

After their 2024 appearance, Brood XIII and Brood XIX won’t synchronize their cycles again for another 221 years. These cicadas, which spend the majority of their lives underground, emerge after 13 or 17 years to mature and engage in a month-long mating process. This event is set to begin in late April in certain areas, triggered when the soil temperature reaches about 64 degrees Fahrenheit.

Brood XIII’s emergence is mostly expected in the Midwest, including Illinois, Wisconsin, Ohio, and Iowa, while Brood XIX has a broader range across Missouri, Illinois, Louisiana, North Carolina, Virginia, and Maryland. The sheer number of cicadas and their distinctive mating buzz, as loud as a motorcycle or jackhammer, promise to make this a memorable natural spectacle.

Though harmless to humans, the sheer volume of cicadas can be overwhelming, leading to mixed reactions from fascination to annoyance. Kritsky, who developed the Cicada Safari app for citizen scientists to document sightings, anticipates both eager spectators and those planning to escape the noisy invasion.

As the cicadas surface in waves across the affected regions through May and June, their lifecycle on the surface is brief but intense, lasting around six weeks. Scientists, including Kritsky, are especially interested in mapping their distribution to study their adaptation and potential cross-breeding between the broods.

This dual emergence offers a unique opportunity to witness and participate in a natural event that bridges centuries, emphasizing the cyclical and interconnected nature of life on Earth.