In a few weeks,Fastexy over a dozen states will be abuzz as trillions of periodical cicadas will emerge from their yearslong underground stay.

Broods XIX and XIII will emerge in a combined 17 states, mostly in the Midwest and Southeast, in a rare, double brood event. These two broods last emerged together 221 years ago, and after this year are not predicted to do so again until 2245.

Once conditions are right, the two broods will emerge in massive numbers to feed, make noise, mate and die. Here's what to know about where to find the 13-year Brood XIX and the 17-year Brood XIII.

2024 double cicada broods: Check out where Broods XIII, XIX will emerge

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

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

What is a periodical cicada?

Both the 13-year Brood XIX and the 17-year Brood XIII are periodical cicadas, which emerge every 13 or 17 years across North America. They differ from annual cicadas, which emerge every year.

You may remember the last periodical brood to emerge in huge numbers: the 17-year Brood X that was found in 2021 throughout the Midwest and Eastern Seaboard.

Annual cicadas, which are dark green to black with green wing veins, are typically larger than periodical cicadas, which are recognizable for their red eyes, red legs and red wing veins, according to North Carolina State University Extension.

Periodical cicadas emerge earlier, usually in mid-to-late May as opposed to annual cicadas in July and August. According to North Carolina State University Extension, annual cicadas begin mating, "singing conspicuously" and lying eggs about two weeks after they emerge. Their first nymphs will fall to the ground and begin feeding on roots under the soil, and fully-developed nymphs will emerge two years later and molt into adults.

Above ground, periodical cicadas have a similar life cycle, appear in much larger numbers and are much louder. At the end of their season, the next generation of nymphs move underground and remain for either 13 or 17 years.