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The mass emergence that comes when these two broods dig up from beneath the ground will be a far cry from the annual occurrences, David Althoff, a professor at Syracuse University's Department of Biology, told ABC News. Residents in about a dozen states from Maryland to Oklahoma, and from Illinois to as far south as Alabama and Georgia, can expect to see cicadas from these periodical broods, according to the University of Connecticut's Periodical Cicada Information Pages.
Brood XIX, the largest geographic extent of all periodical broods, surfaces every 13 years, while Brood XIII emerges every 17 years.
The last time these two broods emerged together was in 1803 when Thomas Jefferson was president of the U.S.
The next time they will co-emerge is not expected for another 221 years, until about 2245, forecasts show.
When multiple periodical broods surface at once, it's typically in different parts of the country, Keith Clay, a professor at Tulane University's Department of Ecology and Evolutionary Biology, told ABC News. An adjacent emergence of two large broods is rare.
"It's just a statistical anomaly, like Halley's Comet," Clay said.
https://abcnews.go.com/US/cicadas-coming-expect-double-brood-emergence-trillions-breeding/story?id=108856097