Much like an unexpected free dinner will distract you from the leftovers sitting in your fridge, this summer’s cicada emergence will turn predators away from their usual prey. During the 2021 Brood X emergence, Zoe Getman-Pickering, a scientist in Lill’s research group, found that as birds swooped in on cicadas, caterpillar populations exploded. Spared from birds, caterpillars chomped on twice as many oak leaves as normal—and the chain of effects went on and on. Scientists can’t possibly study all of them. “The ecosystem gets a swift kick, with this unexpected perturbation that changes loads of things directly,” says Louie Yang, an ecologist and professor of entomology at UC Davis.
From birth to death, these insects shape the forest around them. As temperatures rise in late April, pale, red-eyed cicada nymphs begin clawing pinky-sized holes in the bottom, preparing for his or her grand May entrance. All of those tunnels make it easier for rainwater to maneuver through the soil, where it may well then be utilized by plants and other dirt-inhabiting microbes. Once fully grown and aboveground, adult cicadas shed their exoskeletons, unfurl their wings, and fly off to spend their remaining 4 to 6 weeks on Earth singing (in the event that they’re male), listening for the sexiest songs (in the event that they’re female), and mating.
Mother cicadas use the metal-enhanced saws built into their abdomens—wood-drilling shafts layered with elements like aluminum, copper, and iron—to slice pockets into tree branches, where they’ll lay roughly 500 eggs each. Sometimes, all of those cuts cause twigs to wither or snap, killing leaves. While this might permanently damage a really young sapling, mature trees simply shed the slashed branches and carry on. “It’s like natural pruning,” Kritsky says, which keeps hearty trees strong, prevents disease, and promotes flower growth.
Once mating season winds down, so does the cicada’s life. “In late summer, everybody forgets about cicadas,” Lill says. “They all die. They all rot in the bottom. And then they’re gone.” By late June, there will likely be hundreds of thousands of kilos of cicadas piling up at the bottom of trees, decomposing. The smell, Kritsky says, “is a sentient memory you’ll always remember—like rancid Limburger cheese.”
But these stinky carcasses send an enormous pulse of food to scavengers within the soil. “The cicadas function reservoirs of nutrients,” Yang says. “When they arrive out, they release all this stored energy into the ecosystem,” giving their bodies back to the plants that raised them. In the short term, dead cicadas have a fertilizing effect, feeding microbes within the soil and helping plants grow larger. And as their remnants make their way into woodland ponds and streams, cicada nutrients are carried downstream, where they could strengthen aquatic ecosystems far beyond their home tree.
They may smell like bad hamburgers, but Yang says that for those who’re lucky enough to host a tree stuffed with cicadas this yr, it’s best to only leave their bodies alone to decompose naturally. “They’ll be gone soon enough,” he says. If the pileup is particularly obtrusive, simply sweep them out of the best way and let nature do the remainder.
The considered billions of screeching insects in your backyard might make your skin crawl, but you don’t should be a passive observer once they arrive. Researchers are clamoring for citizen scientists to send in photos of their local cicadas to assist map the upcoming emergence. The Cicada Safari app, developed by Kritsky, received and verified 561,000 cicada pics through the 2021 Brood X emergence—he hopes to get much more this time around.
“This is an incredible natural phenomenon to wonder about,” Lill says, “not something to be afraid of.”
