Billions of cicadas will appear this year in a rare occurrence that hasn’t been seen in the United States since Thomas Jefferson was president and won’t be seen again until 2245, entomologists say.

According to scientists, 2024 will see a rare event called “double brood emergence,” in which two different broods of cicadas — one that appears every 13 years and another every 17 years — emerge simultaneously. The 13-year group, known as Brood XIX or the “Great Southern Brood,” is the largest periodical cicada brood, stretching across the southeastern United States. Brood XIII, the “Northern Illinois Brood,” emerges every 17 years.

The double emergence of Broods XIX and XIII is rare, occurring only every 221 years. These two broods haven’t been above ground during the same time since 1803, and after this year, they won’t be reunited until 2245.

While cicadas are harmless, scientists have warned that the noise levels from millions of cicadas can be more than just a nuisance. A single cicada’s sound, measured from a distance of 50 centimeters, can reach almost 105 decibels. Male cicadas can hit 100 decibels, which is almost like standing right next to a chainsaw.