Cicadas Are Here in St. Louis, and Here's What You Need to Know

By Zachary Linhares on Mon, May 13, 2024 at 10:28 am

PHOTO BY ZACHARY LINHARES

Cicadas sit atop of the leaves on a hydrangea plant on Thursday, May 9, 2024, in Chesterfield.

The cicada invasion is in full swing across the St. Louis region. Billions of cicadas are emerging from the ground — up to 1.5 million per acre.

Kasey Fowler-Finn, an associate biology professor at Saint Louis University, specializes in insect acoustic communication, which makes her an expert in cicadas. She says there are four species that are part of the 13-year periodical cicadas, including the brood emerging underneath our feet: Brood XIX.

Cicadas spend roughly six weeks in egg form before they hatch and burrow two feet underground. There they attach themselves to root systems where they will drink the sap and feed on the roots for the next 13 years, though broods vary on the amount of time they spend underground. When the cicadas arise, they climb trees, molt, sing in a chorus with each other, mate and die. The average life span after emergence is only six weeks.

Scroll down to learn more about cicadas — and see some of the ones we’ve spotted around St. Louis lately.

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PHOTO BY ZACHARY LINHARES

Although cicadas pose no threat to humans, Fowler-Finn says there are some significant environmental consequences to an emergence event like this. The cicadas aerate the soil, while their decomposing shells also contribute to the nutrient cycle in local ecosystems. They also play a necessary role in nourishing snakes, rodents, turtles and more.

PHOTO BY ZACHARY LINHARES

A cicada sheds its shell while clinging to a tree on Thursday, May 9, 2024, in Chesterfield. Fowler-Finn says it is unclear why they spend 13 years underground, though there are two leading hypotheses.

“The combination of the long life periodicity and synchronization can arise from glacial cycles or avoidance to predators,” Fowler-Finn says. “But there is no real good answer at this point.”

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PHOTO BY ZACHARY LINHARES

The cicadas emerge based on soil temperature. So if you haven’t seen any cicadas around you, don’t worry — things just need to warm up.

“We know urban heat islands tend to warm faster, it has to do with local climate,” Fowler-Finn says.

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PHOTO BY ZACHARY LINHARES

Once the brood emerges, they climb trees for protection. Cicadas are most vulnerable when they are molting, and the trees provide them with a secure spot where they can break through their shells without falling.

Once freed from their shells, Fowler-Finn says the cicadas sing the chorusing songs that will be heard throughout the summer.

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PHOTO BY ZACHARY LINHARES

That is only one of the songs the males sing.

“Once they locate a receptive female, by listening for a female response to their call, which is a wing flick, it sounds like a little snap,” Fowler-Finn says. “They then convert to a courtship song; the male and female will do that back and forth until a pair formation, or she rejects them.”

If you want to play a joke on the noisy critters, Fowler-Finn suggests walking up to a tree and snap your fingers: The males will start singing in response.

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Cicadas can also be infected by a zombie fungus, making them real-life Night of the Living Dead creatures.

“There’s a fungus in cicadas that's like a zombie fungus,” Fowler-Finn says. “It basically hijacks the nervous system and makes the insects crawl to a place where they can spread the fungus spores.”

The fungus works by first infecting the male cicadas, then making their wings flap like a female. Thinking they are hearing the sounds of a potential mate, the non-infected male cicadas will try to mate with the infected and spread the spores.

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PHOTO BY ZACHARY LINHARES

“It turns out that birds switch their diets almost entirely on the periodical cicadas for the six weeks that they’re out,” she says. “That has several consequences; it actually releases other insects from predation.” The abundance of food can cause an increase in the bird population for the next year, which then causes a crash when that food source is no longer there. Up the food chain, humans benefit from the massive brood.

“There tends to be turkey booms right after periodical cicadas,” she says.

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