This spring, trillions of cicadas will emerge from the ground in multiple states, part of a rare, double-brood event that hasn't happened in over 200 years.

Two broods, or groups, or cicadas will emerge in over a dozen states: The 13-year brood Brood XIX and the 17-year Brood XIII. According to the website Cicada Mania, Brood XIX will be found in 14 states across the Southeast and Midwest, and Brood XIII will be in the Midwest. The two broods will likely overlap in Iowa and Illinois.

The two broods will begin to emerge when the soil 8 inches underground reaches 64 degrees, and are often triggered by a warm rain. They will likely emerge beginning in mid-May and last through late June.

Whether you're excited or dreading the return of cicadas in the coming months, here's where the two broods will emerge.

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The two broods will emerge in a combined 17 states across Southeastern and Midwestern states, with an overlap in Illinois and Iowa. They will emerge once the soil 8 inches underground reaches 64 degrees, beginning in mid-May and lasting through late June.

The two broods last emerged in 1803, and the next double-emergence is predicted in 2245.

What is the life cycle of a cicada?

Cicadas have the longest life cycle of any insect, waiting 13 or 17 years to emerge, but once they're above ground, things move pretty fast. Female cicadas lay eggs in trees, which drop to the ground and burrow, waiting for years to emerge, depending on their brood.

Once they emerge, adults cicadas will mate, lay millions of eggs and die, all in about five weeks.

What is the difference between annual and periodical cicadas?

Two types of cicadas are common in eastern U.S.: Annual and periodical cicadas. Annual cicadas emerge every year, while periodical cicadas emerge every 13 or 17 years, according to the U.S. Environmental Protection Agency.

Are cicadas harmful to humans or pets?

Cicadas are not harmful to humans, pets, household gardens or crops, the EPA says, and despite their overwhelming numbers, can actually provide a few environmental benefits.

They provide a valuable food source for birds or other predators, can aerate lawns, improve water filtration and add nutrients into the soil as they decompose.