The cicadas are coming, the cicadas are coming
By Nicole Rivard
After a devastating 2020, we all need things to look forward to.
If you’re a naturalist and live in the eastern United States, you are in for a treat late April through early June as one of nature’s great marvels unfolds.
Millions of cicadas are expected to emerge after spending 17 years underground. These periodical cicadas are known as Brood X—they are all black with orange wings and legs and red eyes. Periodical cicada swarms are endemic to the eastern United States, emerging in consecutive life cycles known as broods based on their geographic location.
“The biggest misconception that people have is that periodical cicadas are flying in from somewhere. But they are not,” John Cooley, a cicada expert at the University of Connecticut, told me. “They’re always there. They’re part of the forest. It’s a really cool thing.”
They’re so cool, that Jim Costa, a longtime biology professor at Western Carolina University, believes it’s worth a road trip to see them. Periodical cicadas from Brood X will emerge in Delaware, Georgia, Illinois, Indiana, Kentucky, Maryland, Michigan, North Carolina, New Jersey, New York (extinct or nearly so), Ohio, Pennsylvania, Tennessee, Virginia, West Virginia, and Washington D.C.
Cicadas will begin to emerge when the soil 8″ beneath the ground reaches approximately 64 degrees Fahrenheit. A warm rain will often trigger an emergence. Back in 2004, people began reporting Brood X emergences around May 13, but if the weather is warmer, it might start in late April, according to reports.
“Being an entomologist, I especially nerd out on these things,” Costa told the Smoky Mountain News recently. “It’s one of nature’s great, amazing, natural phenomenon, this mass emergence and the air just alive with this constant loud droning humming sound.”
The sound is created by males sitting high in the treetops using the ridged membranes on their abdomens called tymbals to attract a female to breed with. Soon after mating, females split the bark of living trees and shrubs and deposit their eggs, usually between 24 and 48 at a time. Females can mate many times during an emergence, which can last four to six weeks, and may lay up to 600 eggs before their death.
The eggs remain in the trees for six to 10 weeks, at which point the juveniles hatch, drop to the ground, and burrow into the soil, where they will remain for another 17 years.
Preparing for cicadas
So, what are the cicadas doing underground for 17 years? They are drinking from plants and growing, Cooley said, adding that their emergence is their “grand finale.”
Some people may not be excited about this upcoming performance because they erroneously think periodical cicadas will do extensive damage to their trees.
The truth is cicadas are harmless to humans and pose little to no threat to mature trees. Saplings or small recently transplanted trees such as fruit trees are at a greater risk because their trunk diameters are small enough that egg slits made in the trunk by females may result in the tree snapping.
However, there’s an easy solution. “What we encourage people to do if they have a delicate tree or a fruit tree is to cover them with avian netting when cicadas are active, ” says Cooley, “That just encourages them to move on. The females are not going to be persistent. They will take off and go somewhere else to lay eggs. Cheesecloth is a cheaper option.
Never use chemical insecticides, Cooley says. They can poison animals who try to eat cicadas and inflict unnecessary harm on ecosystems.
“You really could never spray enough pesticides to get rid of the cicadas,” Cooley says. “It’s estimated that 1.5 million cicadas can emerge per single acre of land You can’t be spraying that kind of pesticide out there because you will kill everything in sight.”
A niche to fill
Speaking of ecosystems, cicadas play an important role. Dan Mozgai, a cicada enthusiast who runs the website cicadamania.com, says he gets asked a lot about the “purpose” of cicadas.
They fit into the bigger picture of ecosystems like all living things, he explains. Trees feed off the sun and nutrients in the soil, cicadas feed off the trees, and animals such as songbirds, skunks, raccoons, frogs, snakes, squirrels and possums eat cicadas.
The Ecological Society of America calls what periodical cicadas create in the areas where they emerge and die off “resource pulses.” The massive release of food and energy that comes from a cicada emergence results in an explosion of foraging animal populations, which in turn results in a boon for alpha predators as well.
The sudden scattering of cicada carcasses floods the ecosystem with a short-term, large-magnitude influx of nutrients, and scientists have documented an array of changes that can accompany these pulses.
“When the cicadas die, it’s like dumping bags of fertilizer around the roots of the trees. The extra nutrients should result in a spurt in tree growth and seed production the following spring, which could result in an increase in tree populations and acorns,” Mozgai writes.
Why Brood X comes out every 17 years is still a mystery. Some experts believe the adaptation arose to avoid predators. Other believed it happened in response to glacial cycles, a way to cope with ice ages.
“I have to be honest with you—every hypothesis presented about why they are on this cycle has some huge flaw with it. Each one can pretty much be directly contradicted by some observation you can make,” Cooley said.
Speaking of observations, you can help Cooley with his cicada research by reporting sightings via the Cicada Safari app. Simply download the free app from the Apple app store or Google play, then go on a safari to find periodical cicadas. Photograph and submit the periodical cicadas to Cicada Safari, and after the photos are verified, they will be posted to the live map.
Cooley is studying speciation, the evolutionary process by which populations evolve to become distinct species. His favorite thing about periodic cicadas is if you learn how to crack their signals, you can interact with them.
“They are an accessible insect. Many people have insectophobia and they are a great way to get over that,” he says.