Cicada invasion may be sparse in Iowa County

MARENGO — For all the hype, Iowa County residents may not see — or hear — the massive cicada emergence other parts of the country will experience.

“We may miss Brood XIII and Brood XIX emergence,” Iowa County Conservation Director Jacob Slings said Monday. Brood XIII are 17-year cicadas; Brood XIX are 13-year.

The insects will be hatching any day to the north, if they haven’t already, said Slings. Indiana and Illinois are expected to see both broods at the same time.

“We have not seen any around our area,” said Slings. “In fact, we were discussing today how we haven’t heard any this year.”

If and when the cicadas do emerge, they’ll be molting on the trunks of trees, said Slings. Anyone wanting to find them should look there.

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Once they shed their exoskeletons, they’ll be flying “just about everywhere,” Slings said, but the best place to find them is around trees.

University of Iowa biology professor Andrew Forbes told Iowa Radio in April that Iowa will see only one brood emerge. Illinois is about the only state expected to see both at the same time, he said.

The Cedar Rapids area will see 17-year cicadas, said Forbes. The far southeastern part of the state will see the 13-year cicadas.

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The last time the broods emerged at the same time was in 1803, when Thomas Jefferson was president. They won’t emerge together again for another 221, according to Johnson County Conservation’s newsletter, Conservation Connection.

The offspring of the locusts that emerged 17 years ago have been waiting about eight inches underground, feeding on sap from the root of trees. They move short distances, creating small tunnels between roots.

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If the trees they are feeding on die, they may not survive, Conservation Connection says. The 2020 derecho may have affected the brood’s population for that reason.

The emergence is not an exact science, according to Conservation Connection. Some insects may have emerged last year. Others may not show up until 2025.

The cicadas emerge when soil temperatures reach a steady 64 degrees. They live a few short weeks.

The 17-year cicadas look similar to the “dog day” cicadas that emerge every year in July and August, Johnson County Conservation says.

Brood XIII will live four to six weeks. The males will buzz loudly and incessantly to attract mates. The sound is created by expanding and contracting a membrane called a tymbal.

The females will lay eggs into small, woody twigs. Her offspring will burrow into the ground for another 17 years.

Unlike locusts, cicadas are not a threat to us or to agriculture, said Conservation Connection.

They can damage some hardwood trees, such as oak, hickory, apple, birch or dogwood, according to the U.S. Forest Service. Females create slits in tree branches to lay their eggs. This can weaken branches and cause leaves to die and stems to break.

According to the U.S. Forest Service, literally trillions of the insects will emerge. The sheer number will cause their buzzing to reach 90-120 decibels, equivalent to a gas-powered lawn mower or motorcycle.

Unlike some other insect species, cicadas “sing” during the day, not at night.

Though the insects can be creepy and annoying, they can’t significantly harm humans, according to the Forest Service. They have no biting mouth parts.

Cicadas use a piercing-sucking mouthpart called a rostrum to feed on plant xylem in plant stems and roots.

There are 12 recognized 17-year broods and three 13-year broods. Some studies estimate more than a million cicadas per acre. The large numbers mean that predators can’t kill them all, which ensures the survival of the species.

“If they do emerge in great numbers [in Iowa County], make sure to have plenty of windshield washer fluid handy,” said Slings. “Otherwise, sit back and enjoy the sounds of summer.”