From North Carolina to Connecticut, billions of creatures with eyes the color of blood and bodies the color of coal are crawling out of the earth. Periodical cicadas are emerging en masse, clambering into trees and singing a shivering chorus that can be heard for miles.

What makes this emergence truly remarkable, however, is how long it’s been in the making. This month’s army of periodical cicadas was born in 1996. Their mothers laid their eggs in the branches of trees, where they developed for a few weeks before hatching and heading for the ground. “They just jumped out and rained down out of the trees,” said Chris Simon, a cicada biologist at the University of Connecticut.

Those Clinton-era larvae then squirmed into the dirt and spent the next 17 years sucking fluid from tree roots. Now, at last, they are ready to produce the next generation. The adult males are snapping rigid plates on their abdomens to produce their courtship song. The females are clicking their wings to signal approval. They will mate and then die shortly afterward. Their time in the sun is short, but their 17-year life span makes them the longest-lived insects known.