Expecting a trillion visitors in a cicada '' dual emergence '' : In a rare occurrence, a trillion cicadas from two different broods are expected to begin appearing in the Midwest and Southeast regions of the United States at the end of April.

It's the first time since 1803 that Brood XIX, or the Great Southern Brood, and Brood XIII, or the Northern Illinois Brood, will appear together in an event known as dual emergence.

Thomas Jefferson was president the last time that the Northern Illinois Brood's 17-year-cycle aligned with the Great Southern Brood's 13-year period. After this spring, it'll be another 221 years before the groups, which are geographically adjacent, appear together again.

A roughly 16-state area will be a certain stage for these periodical cicadas, which differ from those that appear annually in smaller numbers.

Forested areas, including urban green spaces, are more likely to have higher numbers of cicadas than agriculture regions.

To put into perspective just how many of these bugs could emerge, one trillion cicadas, each just over an inch long, would cover 15, 782, 828 miles [ 25.4 million kilometers ] if they were placed end-to-end, said Floyd W. Shockley, an entomologist and collections manager at the Smithsonian National Museum of Natural History.

The first are expected to start emerging late this month. Temperature determines when they come out, said Gene Kritsky, a retired professor of biology at Mount St. Joseph University in Cincinnati, and the author of several books on cicadas.

Professor Kritsky said that first the soil needed to reach 64 degrees Fahrenheit [ almost 18 degrees Celsius ], about six inches deep, and '' then you get a good soaking rain, and that's when they really pop.''

They'll use their forelegs to tunnel out from the earth, their beady red eyes looking for a spot where they can peacefully finish maturing.

A few days after they emerge and molt, the males will start buzzing in an effort to find a mate, a slow-building crescendo of noise that as a chorus can be louder than a plane. [ Aimee Ortiz ]


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