In a restored savanna habitat behind the Lake Forest College science center, professor Sean Menke crouched down next to a small circular hole and stuck a thermometer into the ground.
After a short wait, he took the device out to look at the temperature. “That was 52 (degrees), so that’s great.”
The hole was, presumably, a periodical cicada’s tunnel dug ahead of this summer’s emergence of billions of others that will come out simultaneously across the United States. They belong to Brood XIX, four species that appear every 13 years in the Southeast, and Brood XIII, three species that appear every 17 years in northern Illinois.
Since earlier in the week, Menke has been monitoring soil temperatures which, once reaching 64 degrees at 8 inches, should signal the cicadas that they can come out to mate.
“With the weather we’ve been having, there’s some concern that they’re going to be emerging earlier,” Menke said. “And we’re hearing reports from people that they’re finding the tunnel(s) that they dig in the Chicago suburbs.”
Yet despite recent reports of cicadas coming out, experts say the insects probably won’t do so en masse in Illinois for another few weeks, as early as mid-May, but more likely toward the end of the month. Reports of sightings are likely individual “stragglers” that have come out too early or from people who have taken a shovel to the ground.
“It looks like people have been kind of digging them up instead of finding them actually coming out on their own,” said Christopher Dietrich, the Illinois State entomologist.
That still indicates cicadas are readying themselves and close to the ground’s surface. Menke has seen it with his own eyes: He was recently gardening in his yard when his wife accidentally dug one up.
The historic occurrence has generated much excitement among experts, bug enthusiasts and the general public.
Illinois will soon be cicada central when 2 broods converge on state in historic emergence
It will be the first time in 221 years that these two specific broods come above ground at the same time and in such proximity. The last time this happened was in 1803 when Thomas Jefferson was president, and Illinois had yet to become a state. The broods will not necessarily overlap but emerge adjacent to each other in the Springfield and Urbana-Champaign areas.
In the United States, there are 15 broods of periodical cicadas, each of which dig their way out from underground on different 13-year or 17-year cycles. Other broods have emerged at the same time in the past decade but not in the same place. Experts consider this year unusual because two broods are co-emerging in neighboring areas in Illinois for the first time in more than two centuries.
Simultaneous emergence
Stephanie Adams, plant health care leader, displays 17-year-old cicada nymphs, and a chimney, at the Morton Arboretum in Lisle on April 30, 2024. Hundreds of young and vulnerable trees are being covered in fine-mesh netting at the Morton Arboretum to protect them from the imminent cicada emergence. (Antonio Perez/Chicago Tribune)
After a relatively warm winter, there’s been a lot of talk about whether this year’s periodical cicadas might come out earlier than in the past. In Illinois, they have usually emerged around the last week of May or the first week of June.
“It’s hard to predict exactly,” Dietrich said. “Because not only have we had relatively warm temperatures through the winter, but there’s also been a lot of fluctuations in the temperature extremes: from extremely warm days to very cold days.”
Historically, very cold winter and spring seasons have pushed some cicada emergences to happen a few weeks later. But it has rarely happened significantly earlier in a given year.
“It’ll be early, but not super early,” said Mark Hurley, an environmental educator with the Lake County Forest Preserves. “What’s going to pull them out of the ground is soil temp, but also they need the leaves to be out on the trees because it’s that nutrient source going up to the leaves that triggers them to emerge.”
Biologists believe cicadas keep track of the passage of time and years as they feed from a tree’s sap, using a molecular mechanism that allows them to sense patterns from the seasonal flow of water through the tree.
Once ready to mate after their long periods of development, billions of mature periodical cicadas use soil temperature as their main cue to time their simultaneous emergence, ensuring that their sheer numbers overwhelm possible predators and that their species survives.
“There’s a lot of research that shows that you don’t want to be somebody, from a cicada’s perspective, that emerges too early,” Menke said. “Because if you emerge too early, you’re just going to get eaten.”
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Two researchers interviewed by the Tribune earlier this year, John Lill and Martha Weiss, have studied how large numbers of periodical cicadas in emergence years can disturb food chains by providing birds more food than usual; the numerous noisy insects distract avian predators from their usual caterpillar prey, which then feed on oak trees unchecked.
Stages of 17-year cicadas are shown in 1939 in Flossmoor in a Chicago Tribune info-graphic. (Chicago Tribune historical photo)
Smaller, unlikely predators might also feast on periodical cicadas.
An ant expert and the college’s chair of biology, Menke will be joined by Lill and Weiss this summer in studying ant feeding patterns during a cicada emergence. Menke said he expects the small insects will feed on the adult cicadas that aren’t able to successfully molt or shed their shells — becoming a “juicy smorgasbord” for the ants — or on the tiny nymphs or young cicadas that will hatch a few weeks later, which will be “like popcorn falling from the sky — but really nutritious popcorn for ants.”
In any case, because their strength is derived from their numbers, cicadas are very particular about coming out when they’re all ready.
According to Hurley, the mature cicada nymphs that people have been finding in the Chicago area are not yet ready. In a new summer exhibit to celebrate cicadas at the Bess Bower Dunn Museum of Lake County, Hurley pointed to a mural of a ghostly white cicada shedding its exoskeleton with two black spots on its thorax.
“All of our nymphs right now don’t have those patches yet,” Hurley said.
The black spots are crucial for emerging cicadas to have as they allow them to simulate a bigger size and, like a football player’s face paint, create a threatening presence that protects them in this vulnerable phase from predators above ground.
That’s not to say individual cicadas can’t come out by themselves.
“You may start to see a few here and there, over the next couple weeks, coming out locally,” Dietrich said. “But the real mass emergence probably isn’t going to happen until closer to the end of the month.”
Plants and animals
A Brood XIII cicada waits for its wings and new exoskeleton to dry and harden after climbing and molting on a tree in a front yard in Homewood on May 22, 2007. (E. Jason Wambsgans/Chicago Tribune)
At the museum in Lake County, Hurley pressed a button to play the recording of a cicada call.
“That’s the one you hear the most, the ‘pha-ra-oh,’” he said enunciating the syllables to match the pace of the insect’s song. It’s from the so-called Pharaoh cicada, a species of periodical cicada from Brood XIII in northern Illinois.
This cicada species and its unique call — no doubt echoing Biblical accounts of ancient Egypt — became known among early European colonists as the 17-year locusts, further perpetuating the misconception that, like the grasshopper plagues in the Mediterranean and North Africa, cicadas in North America can be devastating to crops and cause famine.
Cicadas are harmless to crops and the vast majority of plants. They are also not dangerous to humans: They don’t bite or sting, and they won’t try to lay eggs on a person. “People aren’t at risk unless they look like an oak tree,” according to the Ohio State University Extension.
The Bureau of Forestry from the city of Chicago’s Department of Streets and Sanitation said in a news release earlier this month that small, brown leaves appear on tree branches that are damaged by cicadas.
This damage is caused by the female insects laying their eggs inside tree branches. Saplings or trees with a diameter smaller than 2 inches in areas with big cicada populations might be harmed, stunting their future growth. But most trees easily bounce back.
To protect small saplings, gardeners can cover the plants with netting for a couple of weeks; the Morton Arboretum recommends postponing the spring planting of young trees.
Experts also suggest that gardeners don’t use pesticides because they often have no effect on cicadas and might poison birds and other animals that feed on dead cicadas.
In the June 10, 1922 edition of the Chicago Tribune, Norman Ekstrom is shown with 17-year cicadas on himself in Geneva. (Chicago Tribune)
“There’s a lot of people that want to make money off of fear,” said Menke’s research colleague Lill, a biology professor at George Washington University, in a previous conversation with the Tribune. “They’re trying to sell pesticides, and the worst thing you could do is spray a bunch of chemicals on your yard because you’re scared of cicadas. You’re doing way more harm than good, and you’re not going to really affect the cicadas, to be totally honest.”
Cicadas are not toxic to pets, but problems can occur when a cat or dog snacks on them “like popcorn at a movie,” according to local veterinary clinic BLVD Vet. Those who consume too many may have difficulty digesting the insects, causing stomach pain and vomiting.
In addition, eating “pesticide-laden cicadas” can introduce harmful toxins to a pet’s system and the hard, crunchy shells can be a choking hazard.
And while humans with more adventurous palates might be tempted by a chocolate-covered or otherwise prepared cicada, the Food and Drug Administration has cautioned foodies who are allergic to shellfish not to consume the insects as they are related to shrimp and lobsters.
Where cicadas will emerge
Periodical cicadas spend 90% of their lives underground, for 13 or 17 years, feeding from a tree’s sap off its roots. This means they’ll likely emerge in large numbers around trees that have been around as long — or for longer — than their broods have; trees that are old and sturdy enough to withstand any damage.
Cicadas will also likely come out in communities with older homes where the soil, and the cicada larvae in it, have been undisturbed by new construction, utility work or soil excavation, according to city officials. Outside the city, Dietrich said, cicadas won’t be in areas dominated by prairie or row crops but rather along rivers and other locations with natural, mature forests.
Experts and cicada lovers are spreading the word about the harmlessness of cicadas so that Illinoisans embrace these fascinating insects once they do arrive.
Dietrich said that Illinois is unique in that it has five periodical cicada broods, more than any other state in the country, though they all tend to come out in different years and different areas.
“It’s a really amazing phenomenon, to be able to see these mass emergences, to think about how that happened, what evolutionary processes might have given rise to that,” he said.
