Posted 10:02 a.m. Wednesday, June 30, 2021

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.

The bug that emerges from underfoot every 17 years will make its way to Wisconsin. Entomologist answers common questions.

This spring a chorus of bugs — with their characteristic long and droning buzz — emerged from the ground out East. From Tennessee to New York, billions of cicadas began to take wing to begin a mating ritual they perform only once every 17 years.  This particular group of cicadas, Brood X or the Great Eastern Brood, is just one of several thousand species of cicadas living around the world right now. 

Although this wondrous spectacle of insect behavior did not make it as far northwest as Wisconsin, UW-La Crosse entomologist Barrett Klein explains that southern Wisconsin will have its turn in three years. We can prepare by learning about their lives and maintaining green spaces to protect them, he says. Here Klein answers some common questions about their lives.   

What are cicadas?  

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.  

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

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.  

Where can we find a reliable map of cicada emergence?  

Cicada Mania. 

USDA Forest Service.

What is the cicada life cycle?  

After mating, a female cuts slits in trees and lays eggs in the slits. Nymphs hatch, drop to the ground and burrow 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?  

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.  

What do cicadas do underground?  

Cicadas are quietly growing and sucking on liquid flowing through the roots of plants. 

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.  

How long are periodical cicadas out when they do emerge?  

Periodical cicadas emerge for four to six weeks as adults. 

When and where will cicadas come out in Wisconsin?  

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

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. 

Is there anything to be worried about when it comes to cicadas? Do they bite? Do they cause problems for plants, etc.? 

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.    

Why are cicadas good for the environment?  

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. 

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

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