It’s not a welcomed reunion, but after 17 years the cicadas are set to return to the East Coast.

Insect experts say that starting in mid April to late May, residents from North Carolina to New England will witness the emergence of billions upon billions of the singing insects. For them to emerge, the ground has to be a mild 64 degrees, notes retired Smithsonian entomologist Gary F. Hevel. That's how, even eight inches below ground, the insects know, "It's party time."

“In places where they’re going to be present, it’s going to be spectacular. There could be as many as 1 billion cicadas emerging per square mile,” Michael Raupp, a professor of entomology at the University of Maryland, told 1010 WINS. Translation: Ick!

Cicadas spend most of their lives underground. Near the end of their lifespans they emerge to climb trees, shed their exoskeletons, sing, fly and mate. Both females and males die soon after the females lay their eggs. The next generation will emerge in 2030 to repeat the cycle all over again.

Aside from the mess and the loud mating calls, these swarms of critters are harmless. But their homecoming in the last stage of their lives is unforgettable to those who experience it thanks, in part, to how they serenade whole neighborhoods with their loud chorus of chirping.

"Most people say it is like a science-fiction movie UFO sound,” cicada researcher Dan Mozgai wrote to Yahoo News in an email.

The East Coast, he added, should expect piles of the dead insects around their homes: "They can pile up like dead leaves."

Mozgai also pointed out that in areas where old trees have been removed due to storm damage or new housing developments, cicadas won’t be seen as they "live along the root systems of the trees and need them to survive.”

The cicadas about to spring from the ground are called Brood II, and are offspring from the last cycle that showed up in 1996, reports National Geographic.