How do cicadas know when to emerge? ‘The Indiana Jones of cicadas’ answers your Brood X questions

Countless cicadas have begun to emerge from underground for the first time in 17 years, and they may pop up in a backyard near you.

Brood X cicadas have been spotted in many parts of the country and are expected in at least 15 states: Delaware, Georgia, Illinois, Indiana, Kentucky, Maryland, Michigan, New Jersey, New York, North Carolina, Ohio, Pennsylvania, Tennessee, Virginia and West Virginia, as well as the District of Columbia. 

Since these type of cicadas have not been seen since 2004, some might know little about them or have questions about their presence.

Gene Kritsky might be able to help with that.

USA TODAY hosted Kritsky, also known as “the Indiana Jones of cicadas,” for an “Ask Me Anything” (AMA) session on Reddit about Brood X. A professor of biology and dean of behavioral and natural sciences at Mount St. Joseph University in Cincinnati, Kritsky has published works on cicadas and has rolled out an app this year, Cicada Safari, so everyday citizens can help track cicada sightings across the U.S. 

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Gene Kritsky, dean of the School of Behavioral and Natural Sciences at Mount St. Joseph University, stands with a case of preserved cicadas in his university office in Delhi Township, Ohio, on Friday, April 23, 2021. Kritsky has a collection of thousands of samples, dating back decades. (Photo: Sam Greene/The Enquirer)

Here are some of the best questions and answers from Kritsky’s Tuesday AMA. You can view the full AMA here.

Editor’s note: Some questions have been edited for length and clarity.

Q: Why are you known as the Indiana Jones of cicadas?

Kritsky: I think it relates to my hat, and that I was once locked in an ancient Egyptian tomb.

Q: Is it true loud calls of cicadas can damage human hearing?

Kritsky: Yes, especially if you hold it very close to your ear.

Q: How is climate change affecting cicada life cycles and numbers, etc.?

Kritsky: Climate change impacts the periodical cicadas two ways. First, it causes the cicadas to emerge earlier in May than they have in the past, and second, it may cause the cicadas to miscount the years when they are underground causing them to emerge a year early or even four years early.

Q: How many different periodical broods exist in the US? Do any of them geographically overlap? Do they all seem to have the same number of years between hatchings?

Kritsky: There are 12 different broods of 17-year cicadas and three broods of 13-year cicadas. Some do overlap. For example, Broods X and XIV overlap between the two broods.

It is also possible for a 17-year brood to over lap with a 13-year brood. That will next happen in 2024 in Illinois when Broods XIII and XIX emerge.

Q: Why do periodical cicadas come out in increments of prime numbers?

Kritsky: For many years, it was believed that the long prime number life-cycle was an ideal way to stop predators and parasites intermediate stages to evolve synchrony with the cicadas. There are mathematical models that suggest that is a way to do that.

However, it has been suggested that (if) long prime numbers life cycles was such an ideal way to stop the evolution of predators and parasites, (then) why do we not find more insects with these prime number life cycles?

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Q: I noticed some emerging cicadas didn’t make it; they either died halfway through emerging from their exoskeletons or emerged fully and remained unable to fly until they just died in the street. Is this normal? What are the usual “success” rates? Are 17-year cicadas particularly “unsuccessful”?

Kritsky: That is normal, but the large number of deformed cicadas may not be as large as observed. Successful cicadas that transform to the adult stage with deformities climb to the tops of trees and out of sight, leaving the deformed cicadas down where we see them. Thus, the malformed cicada seem to be the majority.

Q: What are the factors that tell the brood to emerge? Is it just timing or does temperature also factor in?

Kritsky: Periodical cicadas emerge when the soil temperatures reach 64ºF and especially if there is a nice soaking rain.

This past spring there was a lot of concern that the warm March temps would mean the insects would come out sooner. However, the cicadas need to have matured to the point where they have undergone apolysis, the separation of the old nymphal exoskeleton from the new adult exoskeleton. The adult is inside the nymphal skin when the cicadas leave the soil.

Once they have left the soil, and climbed up a vertical surface, then the adult can undergo ecdysis, the shedding of the old nymphal skin. If apolysis has not happened, then the nymph would not emerge from the soil.

Q: What are some less well-known facts about cicadas that you’re dying to share?

Kritsky: A lot of my favorite facts involve history and cicadas. Here is one of my favorites.

The chorusing of the cicadas has been described as being loud, but in 1902, there was a real demonstration of just how loud they could be. President Theodore Roosevelt gave a Memorial Day speech at Arlington National Cemetery that was nearly drowned out by the cicadas. Roosevelt, a barrel-chested man who learned how to yell over a herd of cattle when he was ranching in North Dakota, and who could project his voice over a crowd of 10,000 or more listeners, was no match for the periodical cicadas.

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Follow Jordan Mendoza on Twitter: @jord_mendoza.

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