The red-eyed, shrimp-sized, flying insects don't bite or sting. But they are known for mating calls that produce such a din as to overpower ringing telephones, lawn mowers and power tools.
As nymphs burrowing underground, cicadas suck sap from tree roots. Almost all members of a group, or brood, burst from the ground within a couple days of each other.
They quickly climb the nearest vertical surface to molt and unroll their wings. In some heavily wooded areas, as many as 1.5 million cicadas per acre will crowd onto trees, expert say.
"It's one of the greatest insect emergences on Earth," said Daniel Summers, an entomologist at The Field Museum.
Brood XIII is expected across northern Illinois, and in parts of Iowa, Wisconsin, Michigan and Indiana. Cicadas live only about 30 days as adults, and their main goal is mating.
A single male's shrill courtship call can reach 90 decibels, equivalent to a kitchen blender. And THAT is scaring some people who have outdoor events planned for the next few weeks.
Ravinia Festival, an 103-year-old music festival held north of Chicago, "counterprogrammed" its schedule to avoid classical musicians having to compete with the insects, said festival president and CEO Welz Kauffman.
June will see more pop bands outdoors, a few concerts moved indoors, and a visit from the Mormon Tabernacle Choir. "With 350 voices on stage, they can hold their own against the bugs," Kauffman said.
At the Chicago Botanic Garden down the road, spokeswoman Gloria Ciaccio joked that her advice for brides holding outdoor weddings there will be to put the tent flaps down, and turn the music up.
In Lake Geneva, Wis., hotel concierge Pat Sheahan is worried that no one will sign up for her walks around the lake.
"If these babies are going to be bugging the heck of out everybody, that's no good," she said.
And one Illinois company that provides ice sculptures has turned down several outdoor parties over the next month. That's because of what happened when owner Jim Nadeau delivered a swan statue to a wedding in 1990, during the area's last emergence of the periodical cicadas.
"We put our tray down and immediately the cicadas came off the ground and attacked the ice. Literally, it was a moving sculpture, this big black ugly mass of cicadas constantly moving," said Nadeau, who owns Nadeau Ice Sculptures of Forest Park.
"I don't want to talk myself out of work, but that was just too gross," he said.
The last massive emergence of periodical cicadas was in 2004, when Brood X emerged after 17 years underground in parts of 15 Eastern states. Some broods emerge after 13 years.
They don't harm humans, although they are clumsy and might fly into people. Birds, squirrels and pets, especially dogs, love to eat them, and they are high in protein.
"They're going to have quite a meal. It's going to be like Thanksgiving for them," said Tom Tiddens, supervisor for plant health care at the Chicago Botanic Garden.
The female cicada cuts a slit in tree branches in which to lay her eggs. That can cause premature browning or loss of leaves, or for some smaller branches to split, wither and die.
So Tiddens, an arborist, recommends protecting small or young trees by using tulle to create a balloon shape around them, making sure the fabric is tightly gathered at the trunk. He's already bought roll after roll of tulle for the garden — "It's the first time I've ever been into Jo-Ann Fabrics," he laughs.
Exactly when the cicadas will emerge is a subject of debate, although there is agreement they emerge once the soil temperature is consistently 64 to 65 degrees for several days.
Gene Kritsky, professor of biology at College of Mount St. Joseph in Cincinnati, accurately predicted the 2004 emergence using a formula tied to April temperatures. Using that formula, he predicts the cicadas will emerge on Tuesday.
But Summers, The Field Museum's collection manager of insects, believes recent cool weather has to be taken into account and that the only accurate prediction is that the cicadas will show themselves by June 1.
While people planning outdoor events might be nervous about the cicadas, scientists like Summers are encouraging people in the Midwest not to miss out on a show that comes around only once every 17 years.
The best place to see — and hear — the cicadas will be forest preserves, golf courses and any land where there are older trees where the soil has been undisturbed since 1990.
Freelance writer David Hammond plans to take that advice. He runs the LTHForum, a Chicago-based Internet site devoted to culinary matters, and his "foodie" friends want to see what the cicadas taste like.
The insects are eaten in other parts of the world, with descriptions of the taste ranging from shrimp to canned asparagus to not much at all.
No recipe has been decided upon yet, but Hammond assumes they will be fried and perhaps accompanied by a dip or salsa.
"Honestly, they'll probably go down easier that way," he said. "Who knows? Maybe we'll love it. We may have to travel around the country as infestations occur."