Some cicadas come every summer, announcing their arrival with a high-pitched hum during Fourth of July parades, backyard barbecues and late-night bonfires.
This year, Brood XIII, a group of cicadas that only appears every 17 years, is returning to Riverside, Brookfield and other communities in northern Illinois, southern Wisconsin and northwest Indiana.
These cicadas live underground until their 17-year cycle is up. Many will emerge through May and early June, when the soil reaches 64 degrees at a depth of 8 inches. They’ll be around for about four to six weeks.
While scientists aren’t sure how the cicadas know when 17 years are up, the theory is that they have an “internal molecular clock” that tracks the life cycle and chemical changes of tree roots around them, according to The Morton Arboretum. Cicadas that emerge yearly normally come out in late July and August. Periodic cicadas have a black body, orange or red wings and red eyes.
In forested areas, there will be about 1.5 million of these cicadas per acre, according to The Morton Arboretum. The more developed and populated Brookfield might see fewer cicadas than Riverside with its bountiful green space. New construction in both villages since periodic cicadas last emerged in 2007 could have disrupted the soil, too.
Most cicadas will fly at most a half of a mile in their lifetime, said Grant Jones, Oak Park’s forestry superintendent. Jones said residents who lived in Oak Park the last time these cicadas emerged 17 years ago told him the area definitely had fewer emerge than in neighboring communities.
Cicadas are not harmful to humans, as they don’t bite or sting, but they can produce a lot of noise that residents are likely to notice this spring. The sound you hear is a mating call from male cicadas to attract female partners.
“A lot of people are paying attention and kind of curious about cicadas,” Jones said. “People are usually not used to them being around.”
These insects won’t chow down on trees, but they will drill into smaller branches to lay eggs and continue their legacy. This, unfortunately, can cause small branches to break off or die, Jones said. Trees with a trunk less than two inches in diameter and few branches are likely at the most risk.
“Their main purpose is to reproduce and get the next generation going,” Jones said.
These cicadas typically lay eggs in oak, maple, hickory, apple, birch, dogwood, linden, willow, elm, ginkgo and pear trees, according to The Morton Arboretum. They may also lay eggs in shrubs.
Residents worried about protecting their trees can do so by covering them with mesh netting that prevents cicadas from drilling into them. The netting should have holes no larger than a fourth of an inch, Jones said. This type of netting can be found at hardware stores. Some tree owners even use tulle to protect their plants, Jones said. Openings can be secured with staples, string or zip ties.
“If your little finger fits through a hole, it’s big enough to admit a cicada,” says The Morton Arboretum.
The Village of Riverside recommends pushing off planting any new trees until cicada season is over, as younger trees are more susceptible to being damaged when female cicadas lay eggs due to their smaller size and lower number of branches. The village itself has also covered many public trees with mesh nets, which can be seen around town.
Sprays or insecticides won’t have an impact on cicadas, either, and can even harm beneficial insects, as Riverside notes online. Exclusion through netting is the best way to keep plants healthy from cicadas, Jones said. But cicadas aren’t the only thing that can potentially damage plants.
“As we get into the heat and, often times, dryness of the summer, that’s another good time to make sure that you’re watering your plants properly just to keep them healthy,” he said. “That way, if there is any damage, they’re not also being stressed by a lack of moisture.”
Others might want to wait to plant smaller trees until the cicadas are gone again.
When removing netting, residents should be sure to do so carefully, Jones said. Branches and leaves can get intertwined and damaged easily during this process.
One common question, Jones said, is if pets eating cicadas could be dangerous. Cicadas are not harmful or toxic to pets, he said, but if a pet eats too many, they might get a stomachache.
After the cicadas mate and lay eggs, they will die. According to The Morton Arboretum, “there will be dead cicadas everywhere,” so residents can expect to see them walking or driving around. As they decay, there may be an odor.
Despite the annoyances of dealing with cicadas, Riverside and Brookfield recommend that residents embrace their arrival.
Online, Brookfield has promoted a cicada photography contest hosted by Visit Oak Park. Winners in the three categories — Most Colorful Picture, Most Cicadas in One Picture and Best Action Shot — will each receive a $100 gift card. Participants must live in Brookfield, Riverside, Oak Park or another nearby community; the full list is available on Brookfield’s website.
Riverside is encouraging people to use this time to learn about cicadas.
“This cicada emergence offers a unique opportunity to witness one of nature’s incredible events,” the village said in an online news release. “While it might be a bit inconvenient, it’s a chance to observe these fascinating insects up close. Educating children and community members about cicadas can foster a greater appreciation for our local ecosystem.”