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Over the next few weeks, trillions of cicadas will emerge from underground in over a dozen states. Periodical cicadas, the insects famous for their huge numbers and loud noise, are emerging in two groups, or broods: Brood XIX and Brood XIII.

The two broods, which have not emerged together in 221 years, will appear throughout the Midwest and Southeast. For some, the conditions are already right and the cicadas are beginning to emerge, when they will breed, make noise, eat and eventually die.

Have any cicadas emerged in your state yet, or will they soon? Here's what you should know.

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Are cicadas already out in 2024?

Adult periodical cicadas from Brood XIX have already been spotted by users in multiple states across the Southeast, including Georgia, North Carolina, South Carolina, Alabama, Mississippi, Tennessee, Arkansas, Kentucky and Missouri according to Cicada Safari, a cicada tracking app developed by Mount St. Joseph University in Cincinnati, Ohio.

Through Cicada Safari, users can confirm their sightings of cicadas with pictures, look at a map of other cicada sightings, join a leaderboard with other users and learn more information about cicadas.

2024 cicada map: Check out where Broods XIII, XIX are projected to emerge

The two cicada broods are projected to emerge in a combined 17 states across the Southeast and Midwest, with an overlap in parts of Illinois and Iowa. They emerge once the soil eight inches underground reaches 64 degrees, expected to begin in many states in May and lasting through late June.

The two broods last emerged together in 1803, when Thomas Jefferson was president.

What is a brood?

According to the University of Connecticut, broods are classified as "all periodical cicadas of the same life cycle type that emerge in a given year."

A brood of cicadas is made up of different species of the insect that have separate evolutionary histories. These species may have joined the brood at different times or from different sources. These different species are lumped together under the brood because they are in the same region and emerge on a common schedule.

Why do cicadas make so much noise?

You'll have to thank the male cicadas for all that screeching. Male cicadas synchronize their calls and produce congregational songs, according to Britannica, which establish territory and attract females. There is also a courting call that they make before mating.

Unluckily for us, the 13-year and 17-year brood cicadas are the loudest, partially because of the sheer number of them that emerge at once.