How the cicada phenomenon is affecting the northern Illinois ecosystem

Cicadas emerge every year somewhere in the eastern United States, at either 13-year or 17-year intervals. This year is remarkable because two broods are emerging simultaneously for the first time in 221 years.

Five weeks after their emergence, we find ourselves in the final two weeks of a once-in-17-years phenomenon in northern Illinois.

While the Brood XIII cicadas’ emergence came as a loud and awe-inspired disturbance for us, nature was more than prepared to reap the benefits of the abundant “resource pulse” causing ripple effects in surprising ways throughout our local ecosystem, experts at the Morton Arboretum in Lisle said.

The arboretum’s plant health care lab has been researching the cicada emergence and answering questions from the public on how to best care for their trees. Marvin Lo is the root biology research program manager for the team.

“Some direct effects could be increases in predator populations with a decrease in predation of other insects and prey, increases in soil nutrients, and perhaps more damage to trees from tips of branches breaking,” Lo said.

The 13- and 17-year cicadas will emerge in the same year this spring and summer for the first time since 1803. The dual emergences likely won't overlap, as the 13-year cicadas will cover most of central and southern Illinois while northern Illinois will see the 17-year brood pictured here.

Tips of branches are vulnerable because that is where female cicadas use their razor-sharp ovipositor organ to deposit about 20 eggs at a time. A single female cicada can lay up to 600 eggs before their life cycle is over. Trees will develop a stress response if 20% of their canopy is killed or removed.

Among the predators feasting on the cicadas are squirrels, raccoons, coyotes, foxes, fish and both domestic poultry and wild bird species. It has been predicted birds such as bluebirds, cardinals, woodpeckers and raptors will see a population increase because of the nutrient abundance, according to the Morton Arboretum website. It also is predicted that we may see more rabbits, as their natural predators, foxes and coyotes, fill up on easier-to-catch cicadas instead, according to the arbortetum.

It has been recognized [that] the aeration related to cicada tunneling allows for deeper penetration of water, fertilizers and organic matter. This can improve turf grass growth, [and] I’m sure it has a benefit to all plants.”

—  Stephanie Adams, Morton Arboretum plant health care leader

“[This] will impact the forest down the line,” Lo said. “In a recent study, they found during emergence years of periodical cicadas, predation on caterpillars decreased, resulting in higher herbivory on oak saplings, [resulting in fewer younger oaks].”

At the Morton Arboretum, researchers are investigating in their labs how extra fertilizer from decaying cicadas affects tree and plant growth. Of particular interest is how the excess nitrogen and nutrients affect soil composition and how this alters the interwoven ecosystem for its interdependent species.

“We will be quantifying how much carbon and nitrogen the cicada bodies will be providing to our research plots,” Lo said. “In addition to the chemical analysis of the cicadas, we have long-term monitoring of tree growth and soil nutrients, which may be affected by the pulse of nutrients from the cicadas.”

Stephanie Adams, the arboretum’s plant health care leader, indicated that to see the periodical cicadas’ effects on the ecosystem, sometimes you have to examine a little closer.

“It has been recognized [that] the aeration related to cicada tunneling allows for deeper penetration of water, fertilizers and organic matter,” Adams said. “This can improve turf grass growth, [and] I’m sure it has a benefit to all plants.”

Adams said the emergence of 17-year periodical cicadas will not affect the annual emergence of “dog-day cicadas” that serenade northern Illinois’ summer days every July through September. She stressed the fluidity of nature and the harmony between both annual and multiyear cycles interplaying in coexistence.

“The emergence of periodical cicadas is normal for our ecosystem,” Adams said. “Their emergence and activity create a localized pulse of change just like any other natural event like fire, flooding or a tree falling down. Nature is constantly changing, and living organisms are always adjusting and adapting to new or altered conditions.”