Cicadas are coming: What experts say you should know

Two periodical cicada broods known for their exceptional size are beginning to emerge in Illinois, and experts said it’s the first time the two broods have emerged together since Thomas Jefferson was president.

Matt Bertone, director of the Plant Disease and Insect Clinic and a member of the Department of Entomology and Plant Pathology at North Carolina State University, said it’s been 221 years since this ecological event has taken place.

“This is the first time since 1803 that Brood XIII, mostly in Illinois, and Brood XIX, widespread but mostly in the South, have seen each other. There are other years where two broods emerge, but this is a large combined one,” Bertone said in an email to Shaw Local News Network.

Periodical cicadas are known for hatching from eggs in tree branches and then digging holes in the ground, where they pass through five juvenile stages before emerging from the soil years later.

Brood XIII, known as the northern Illinois brood, emerges from the ground every 17 years, and Brood XIX, known as the great Southern brood, emerges every 13 years, according documents from the University of Connecticut. Although 13-year and 17-year broods emerge at the same time with some regularity – the next occurrence will be in 2037 – it’s rare for two large broods that cover an area adjacent or overlapping one another to emerge at the same time.

They will probably come out next week and, if not, then the week after. [It’s] hard to say, but the lack of ice on some Midwest lakes this winter suggests they will come early [next week].”

—  Chris Simon, University of Connecticut professor

The two broods will combine to cover an area spanning 17 states, but they are not expected to co-occur across a widespread area. In Illinois, Springfield is mostly likely to experience both broods, while DeKalb County and the rest of northern Illinois are more likely to predominately see the Brood XIII later this spring.

University of Connecticut Department of Ecology and Evolutionary Biology professor Chris Simon, whose research focuses on the systematics, evolution and biogeography of cicadas, said the 2024 periodical cicada emergence will be “a wonderful spectacle” and “a fantastic educational opportunity for young people, especially budding biologists.”

Birds and other predators will benefit from the emergence, viewing the periodical cicadas as an additional food source, and dead cicadas will act like fertilizer for the soil, Simon said.

Although the two broods are expected to emerge across a large swath of the country, Simon said that doesn’t mean the entire Midwest and southeast will see large numbers of cicadas at the same time.

“In the South, they started in mid-April, and as you go north, they start later,” Simon said in an email to Shaw Local News Network. “They were already coming out in the St. Louis area two days ago and continue to do so. In northern Illinois and the Chicago area, sightings are still mostly underground nymphs that have not come out yet. They will probably come out next week and, if not, then the week after. [It’s] hard to say, but the lack of ice on some Midwest lakes this winter suggests they will come early [next week].”

Bertone wrote that cicadas emerge when ground temperatures at a certain depth reach 64 degrees, causing the insects to emerge at different times – even within a single brood. Once they’ve emerged, cicadas will be around for about a month before the end of their life cycle.

“Because emergence dates differ in different regions, it’s hard to predict how long they will be active. However, the adults typically only live about three to four weeks, so that can be used to estimate when they will begin to subside after emergence,” Bertone wrote.

Simon said people with small trees should take care to cover them with netting to keep cicadas from laying eggs on the tree, but Simon and Bertone said the periodical critters – capable of making sounds as loud as 90 decibels when in large numbers – are generally not dangerous to humans and vegetation.

“It could perhaps affect some activities, but not a lot,” Bertone said. “Some wood, perennial crops like blueberries, grapes, apples ... are plants that can be affected by cicadas, but it depends on the density of individuals laying eggs in the plants and how much mechanical damage they do.”