Midwest Marvel: Millions of Cicadas Emerge in Rare Phenomenon

They’re not due to emerge until May, but ecologist Carl Strang is so excited about the arrival of millions of periodical cicadas in the Chicago region that he’s searching in April for signs they are coming. Little holes or miniature chimneys in the ground mean the cicadas that have lived as nymphs beneath the earth for 17 years are checking things out, such as soil temperature and other weather conditions, to prepare for their grand entrance, explains Strang, a Warrenville resident, retired Forest Preserve District of DuPage County naturalist and author of a blog covering singing insects.

Sometime in mid-to-late May, these 1.5-inch-long creatures will come out of the ground after dusk to crawl up trees, shed their skins and begin three weeks of frenzied mating, with lots of critters like birds waiting in the ready to eat them. In some places, the sound of their courtship singing will be nearly “deafening.”

These aren’t the annual, or dog-day, cicadas heard droning in mid-to-late summer each year. Rather, these are special broods that live underground for many years before emerging for one big show.

Map of the periodical cicada broods and years of emergence. Photo courtesy USDA Forest Service/map.

In parts of Illinois, two broods will emerge concurrently this year, the 13-year cicadas and the 17-year cicadas. This is a special year because it’s been 221 years since both broods came out at the same time. The last time was in 1803, the year of the Louisiana Purchase.

“The two broods will not overlap in the Chicago region, but only in a small part of central Illinois,” Strang says. Those in the Chicago region will witness the 17-year cicadas.

“Because there are so many of them, it can be something some people just plain don’t like,” Strang admits. “Some people will take a vacation just to get away from it.”

Nonetheless, Strang, who has studied singing insects in the Chicago area for many years, says when the periodical cicadas emerge, folks should plan to see them.

Natural Wonder of Eastern North America

“They have a story that’s unique, odd and interesting,” Strang relays. “It’s a phenomenon that really sets the historical forest part of eastern North America apart from the rest of the world. They’re native. They’re colorful. They’re orange with red eyes. They have an amazing lifestyle. They live all this time under the ground in the dark, then all of a sudden here they are. They all come out and then they’re done until another 17 years.”

Scientists hypothesize that periodical cicadas may have evolved to emerge all at once as a means to overwhelm predators and not all get eaten. They also think they may have evolved at the end of the Ice Age and retreated underground during cold-spell years.

Periodical cicadas this spring will be seen and heard from southern Wisconsin south through parts of Iowa, Illinois, Missouri and Arkansas. They won’t be everywhere. “But they’ll be heavy in the parts of suburbs where forests weren’t cut down for agriculture or in areas where people planted lots of trees years ago,” Strang says.

“In DuPage County, for example, they’ll be thick in the less-developed eastern part, but not the western part,” he predicts, adding he’s read newspaper accounts from the mid-1800s stating that periodical cicadas were once prolific in the western part of the county, but then they vanished, likely due to development.

They’ll especially be present in forest preserves with large, undisturbed old trees such as Ryerson Woods, in Lake County, and Fullersburg Woods, in DuPage County, among many others.

Periodical cicada nymphs emerge at dusk in Fullersburg Woods 17 years ago. Photo by Carl Strang.

Seventeen years ago, Strang visited Fullersburg Woods to search for the tiny holes in April that meant the cicadas were coming in May. “They come to the surface two or three weeks before they actually emerge,” he explains. “They do that to monitor conditions; they don’t want to come out if it’s too dry or too cool. These are nymphs that have lived for almost 17 years underground, using little beaks to suck sap from tree roots. They come out at night and need time to climb up onto something, usually a tree, where they attach their exoskeleton and an adult can emerge.” 

Observing the Emergence

Strang says in mid-to-late May 17 years ago, he visited Fullersburg Woods for several nights to observe the emergence. “One relatively cool night, I started hearing scratching and rustling sounds and thought, ‘Oh boy, here they come.’ But the sounds faded away and they didn’t come out.”

Annual, or dog-day, cicadas are larger than periodical cicadas and lack the red eyes. Photo by Steven D. Bailey.

A few nights later, he heard the scratching sounds again. “And there they were, climbing up on tree trunks or herbaceous plants,” Strang recalls. “They’re not sprinters; they go slowly until they find some place to latch their claws on and shed their skin, revealing a new, soft exoskeleton beneath. You’ll see a split down the back. It takes quite an effort—a couple of hours. It’s as if you had a super-tight piece of clothing on, so tight that it’s almost part of your skin and it’s all over you and you can’t use your hand and you have got to wiggle out of it,” he explains.

They don’t all come out at once. It will take a few weeks for all of them to emerge and build up to the peak of numbers when they’re seemingly everywhere screeching loudly, flying at the tree tops and getting snatched by birds and other wildlife.

“They can collect in certain trees, and if you’re standing under one of them at the peak midday, it can be deafening,” Strang relays. “I started carrying earplugs when I went to the woods 17 years ago.”

After mating, the female uses a saw-like structure on her abdomen to create a little slit underside a twig on the tree or shrub. She lays her eggs and then eventually dies, as do all the other adults, which live for about four to six weeks.

Tree Care

Fredric Miller, senior scientist in entomology at The Morton Arboretum, in Lisle, says mature and healthy trees where cicada eggs have been deposited may show some terminal branch damage called flagging, likely in early August. “This will only result in some natural pruning and is not harmful to the plant,” he says.

However, he suggests waiting to plant young trees and woody shrubs that are less than 2 inches in diameter this year until fall. He also suggests covering vulnerable small trees and woody shrubs with netting. “Make sure to gather the netting around the trunk as near to the ground as possible,” he advises. “Once the emergence event is over, be sure to remove the netting.”

Miller and Morton Arboretum senior writer Beth Botts will present the program Cicadas Are Coming at 6:30 p.m., April 3, at the arboretum (preregister at MortonArb.org/explore/activities/adult-programs/cicadas-are-coming).

Strang and the arboretum do not recommend homeowners use pesticides to control the cicadas.

Those living in neighborhoods with large cicada numbers may have to do some sweeping up and cleaning at the end of the cycle, but Strang says studies show the dead cicadas add important nutrients to the soil. In addition, when the nymphs emerge, they aerate the soil.

Meanwhile, few will notice that millions of miniature eggs are hatching and dropping to the ground as nymphs where they’ll find a crack or hole in the soil to head for their new home for 17 years.

Then in 2041, they’ll take their parents’ places in the trees above the ground to perpetuate their species.

Sheryl DeVore has written six books on science, health and nature, as well as nature, health and environment stories for national and regional publications. Read more at SherylDeVore.WordPress.com.