Posted 8:56 a.m. Wednesday, Feb. 7, 2024

Currently, 3,335 species of cicadas have been described and named. Seven of these are periodical cicadas like the bugs pictured on these leaves. Photo by Gene Kritsky.

Wondrous spectacle of insect behavior to be seen — and heard — in southwest Wisconsin this spring

In spring and summer 2024, billions of cicadas — bugs with a characteristic long and droning buzz —  will emerge together after patiently biding their time underground for 17 years. They will be visible and audible in cities and natural areas spanning a stretch of the U.S. from southern Wisconsin through sections of several states to the south including Iowa, Illinois, Missouri and Arkansas. See the map.

2024 is a special year for the cicada. For the first time since Thomas Jefferson was president, two broods belonging to two different species of periodical cicadas will emerge at the same time, an occurrence that happens only once every 221 years. One brood has been underground for 13 years and the other for 17 years. The exact area of this overlapping emergence of cicada species is unclear, although it will be somewhere in Illinois.  

UW-La Crosse entomologist Barrett Klein will be celebrating their emergence in Illinois with fellow bug aficionados. He says we can prepare by learning about cicadas’ lives and maintaining green spaces to protect them. Here, Klein answers some common questions about the cicadas and their rare emergence.  

When do cicadas come out?  

A large number of cicadas on a tree. Photo by Gene Kritsky, Mount St. Joseph University.

That depends on the species. These particular cicadas to emerge in 2024, belonging to Brood XIII and Brood XIX, are just two of the several thousand species of cicadas living around the world right now. 

Brood XIII and Brood XIX cicadas will emerge in spring and summer 2024. The exact dates are unclear, although scientists predict the most explosive emergence will fall within a two-to-three-week period from mid-May through early June. They could arrive as early as late April.  

Where will the cicadas come out?  

Map of where Broods XIII and XIX occur. Image by Gene Kritsky, Mount St. Joseph University.

Various online maps show the location of the emergence for Brood XIII and Brood XIX, which includes southwestern Wisconsin and several states below, including mainly parts of Iowa, Illinois, Missouri and Arkansas. 

The cicadas will emerge all over — in cities and natural areas. There will be hot spots. The best way to locate those will be through crowd sourcing and media reports. Look to websites like Cicada Safari and iNaturalist for updates. Cicada Safari is a free app that is full of information and will be cicada-seekers' best tool. 

Map of cicada emergence 

Cicada Mania. 

When and where will cicadas come out in Wisconsin?  

Periodical cicadas will emerge as Brood XIII in Wisconsin in 2024.  

Will 2024 be a big cicada year? 

A tree with a large number of branches that have flagged (damaged by cicada eggnests). Photo by Gene Kritsky, Mount St. Joseph University.

Yes! This is the first time in 221 years that two species of cicada, Brood XIX and Brood XIII, will emerge at the same time. The last time both broods came out at the same time was 1803. Brood XIII has been underground for 17 years. Brood XIX has been underground for 13 years.  

What is the cicada life cycle?    

A developing adult cicada sheds its exoskeleton. Photo by Gene Kritsky, Mount St. Joseph University.

Below the ground, cicadas are quietly growing and sucking on liquid flowing through the roots of plants. Nymphs emerge from the earth en masse, climb trees and break out of their old exoskeletons, which includes their foregut, hindgut and tracheae. A new exoskeleton, supple and wrinkled underneath the old, is then exposed, hardening and gaining color over time. 

The males then produce their mating call — the loud buzzing noise — to attract females and mate. After mating, a female cuts slits in trees and lays eggs in the slits. Nymphs hatch, drop to the ground and burrow into the soil to feed on the sap flowing through xylem in plant roots. They develop, slowly growing and molting several times before emerging again one or more years later. Once above ground, they climb, molt one last time, spread their wings, and engage in a reproductive frenzy.   

Why does it take 13 or 17 years for periodical cicadas to come out from underground?  

Cicada nymph that has just emerged. Photo by Gene Kritsky, Mount St. Joseph University

The origin of the trait may have to do with surviving extended cold spells tens of thousands of years ago. As far as why the trait has been maintained, or exists today, is a mystery. Two hypotheses attempt to explain why a periodical cicada brood spends this specific length of time (13 or 17 years), underground. If you spend a large, prime number of years out of the picture, it might be difficult for predators or parasites to synchronize their life cycles with yours and to target you as a host. Only one species of fungus is known to live long enough to coincide with the periodical cicada’s life cycle, and it is easy to spot as fungi replace the abdomens of many a cicada, rendering the cicadas infertile.   

The second hypothesis involves avoiding hybridizing with other cicadas. Were periodical cicadas to emerge regularly alongside other species of cicadas and mate with them, the resulting offspring might lose traits that have made periodical cicadas so successful. Which hypothesis is correct, if either, remains to be determined.  

How long are periodical cicadas out when they do emerge?  

Periodical cicadas emerge for four to six weeks as adults. 

Why do cicadas emerge in broods?   

With millions emerging from the earth simultaneously, no predators could hope to eat them all. A mass emergence helps to ensure that some cicadas will survive.  

What are cicadas?  

Cicada on a tree. These bugs benefit the environment and enrich human culture. Photo by Gene Kritsky.

Cicadas are true bugs (the order of insects with piercing, sucking mouthparts) that sing from the trees during the spring or summer. You can find these all around the world. Currently, 3,335 species of cicadas have been described and named. Seven of these are periodical cicadas living in the eastern U.S. Two other periodical cicadas live elsewhere, but their development only lasts four or eight years. Unlike all other species, periodical cicadas in the U.S. spend a whopping 13 or 17 years underground. Having known a subterranean existence for what amounts to 95.5% of their lives, they emerge when the earth warms during that final year and take to the wing for a mere four to six weeks as adults.  

What is the difference between a locust and a cicada? 

Cicadas, being true bugs, belong to the order Hemiptera, and are more closely related to plant-sucking treehoppers, planthoppers, leafhoppers, and froghoppers (spittlebugs). Locusts, on the other hand, are grasshoppers, jumping insects in the order Orthoptera (along with crickets and katydids) that have a stage during which they aggregate and fly together en masse. They chew their food with mandibles, rather than suck sap from plants using a proboscis. Both cicadas and grasshoppers sing, but cicadas usually do so from the trees in a droning, outrageously loud manner, while grasshoppers are low to the ground and much quieter. Cicadas buzz using their abdomens, and grasshoppers rub leg against wing. 

Cicada sound? 

Cicadas make a loud and droning buzz. Only males sing songs, rattling membranes called tymbals above hollow regions of their bodies that act as resonating chambers. Male periodical cicadas perform in choruses to attract mates and sing a different courtship song when in the presence of females. Females listen, and sometimes respond with wing flicks, inviting males to mate.  

What do cicadas eat?   

As adults, cicadas pierce small tree twigs or bushes to withdraw minerals and some carbohydrates from the water-filled xylem vessels. 

Fungal parasite that kills cicadas?  

There are a good percentage of cicadas that will be killed by a fungal parasite that can match the long life cycle of periodical cicadas. The tip of the cicada’s abdomen pops off and is replaced by fungi ready for dispersal. This changes the song of the bug, causing the male to sing with a higher frequency. Bugs with the parasite also adopt a wing flicking motion that females use when communicating receptivity. This results in calling other males, who come in close contact, pick up fungi, and become vectors themselves. Because so many cicadas arise in one emergence, the parasite is not able to destroy the population of bugs as a whole. Mass emergence in synchrony is likely a big benefit for the mass of cicadas because even after all available predators are satiated, billions remain to continue a legacy of protracted periodicity. 

Why are cicadas good for the environment?  

A shed cicada skin on a piece of grass. Photo by Gene Kritsky, Mount St. Joseph University.

In so many ways, cicadas benefit the environment and enrich human culture. As immatures, they aerate the soil. When they emerge, they are prey (food) for vertebrates and invertebrates alike. When they perish, they enrich the soil. Culturally, humans have been entranced by cicadas for millennia, and they appear in our literature, music and art. They are traditionally eaten by peoples the world over and have been used as symbols of resurrection or happiness. Some people cook with them. Others play music with them. Find your personal connection and embrace this natural phenomenon when you get the chance. 

Is there anything to be worried about when it comes to cicadas?

Cicadas do negligible damage to plants, and no harm to humans. If handled, an adult can slowly attempt to pierce skin with its proboscis, but this does no harm, and no disease has ever been known to be transmitted by a cicada.    

Barrett Klein is an entomologist who studies insect behavior as a professor of biology at the University of Wisconsin – La Crosse. Email bklein@uwlax.edu 

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