2021 cicadas: 13 facts about the Brood X cicada invasion, maps, when they will emerge Posted May 07, 9:30 AM Billions of Brood X cicadas that look like this will be emerging from the ground in 15 U.S. states in May and June of 2021, and making a lot of noise. Facebook Share The big cicada invasion of 2021 has already started in some parts of the eastern United States, and billions of these mysterious red-eyed insects known as Brood X will soon be digging their way out of the ground and flocking to trees in more than a dozen states. The Brood X cicadas have been hiding underground for a very long time — 17 years, to be exact. And now that the soil is warming up, it’s almost time for them to emerge in huge numbers.