Still have questions about cicadas? In this video, we explore the lifespan of cicadas, what they eat and whether they are harmful to humans or pets. | USA TODAY

Wait for it ... billions of Brood X cicada nymphs are emerging from the ground in 15 states — a natural phenomenon that only occurs every 17 years. After feeding off tree roots for nearly two decades, the nymphs crawl out of the soil and climb trees and other vertical structures in search of a suitable place to shed their shells. Molting takes several hours. After it has emerged from its carapace, the cicada must wait several more hours for its body and wings to harden. *** In this time-lapse fo