Land & Conservation

Cicadas Will Disappear as Suddenly as They Came

But there’s a surprising way scientists—and trees—will remember they were here

photo: Adobe

An adult Brood X cicada.

After spending seventeen years growing underground, Great Eastern Brood, or Brood X, cicadas emerged in May by the billions, with a huge showing in the Southeast. “When they come up in these numbers, they satiate every predator—every bird, every rodent, every fish feeds until it can’t eat one more cicada,” says Matt Kasson, who teaches forest pathology at West Virginia University in Morgantown. 

Following a brief and noisy stay above ground to mate and lay eggs, the life cycle of a cicada is complete; they’ll mostly be dead by the end of June, and the next generation will start its own journey.

The cicada’s evolutionary strategy is as bizarre as it is effective. The insects are simply too numerous to all end up as a meal, so enough survive to mate and lay eggs. The seventeen year rhythm assures that other animals won’t come to rely on the emergence. “Predators can predict when periodic insects emerge,” Kasson says, “but there does come a timing sweet spot when enough generations have passed that the collective knowledge is lost.” 

photo: Adobe
A Brood X cicada molts and takes its adult form after emerging from the ground.

For the time they are with us above ground, the noise can be deafening; the brood is actually composed of three different species, and the males call for a mate by flexing a structure called a tymbal and using their abdomens as a resonating chamber. As Kasson points out, “you can’t not notice when they come.” After mating, females lay eggs in trees, and the adult insects then die, their corpses providing a welcome nitrogen boost to the soil (scientists can actually see cicada cycles reflected in tree rings—the extra nutrients mean extra growth in the year of an emergence). 

The eggs hatch after about six weeks, and the white and rice-grain-like nymphs tumble to the ground and start digging using specialized limbs. Once underground, they attach to tree roots and feed on sap (“they tap into a root system like a college kid taps into a keg of beer,” Kasson says), counting seventeen sap cycles—scientists don’t know exactly how, but the fact that seventeen is a prime number might play a role—as they molt and grow.

Meanwhile, the world moves on and forgets, and potential predators move on and forget—until 2038, when the patient nymphs that hatched this year will rise close to the surface and wait for the soil temperature to hit sixty-four degrees. Then they’ll burst up in droves to start the cycle anew.

To see a list of the fifteen states (plus Washington, D.C.) where Brood X cicadas have emerged or are expected, go here; for an interactive map, go here.