You could see millions of cicadas in some parts of Wisconsin this summer. Here's why. (2024)

Cicadas are no stranger to Wisconsin in the summer. Hearing them is often something people associate with long, warm nights outdoors.

Now, imagine thousands or even millions of them all at once. That won't be just a thought in June when 17-year cicadas return to parts of southern Wisconsin after nearly two decades in the ground.

For those curious about the phenomenon, here's what you need to know.

What are 17-year cicadas?

For starters, there are many types of cicadas in North America, according to PJ Liesch, extension entomologist at UW-Madison's Insect Diagnostics Lab, . There are some that we see every year, which we often see in warmer months of summer like July and August. Those have life cycles of around two to three years.

There are also seven periodical species of cicadas in North America: three that emerge once every 17 years and four species that emerge once every 13 years. In 2024, in Wisconsin and other parts of the Midwest, there is a group, or brood, of cicadas known as brood XIII, which is a 17-year periodical cicada.

What makes this event unique beyond it only occurring every 17 years is the sheer number of cicadas. Around June, some parts of the Midwest will see cicadas numbering in the thousands and millions.

Okay, so will all of Wisconsin be overrun by cicadas?

Liesch doesn't expect southern Wisconsin to be overrun by cicadas in June, but certain spots could be.

"Historically, some of the biggest numbers seen have been in the general Chicago area of northern Illinois, but we will have some areas of activity here in Wisconsin, the best known of which will probably be Lake Geneva," Liesh said. "If you're in one of those spots, they can be extremely dense, millions or billions in small areas. You could have maybe 20 to 25 emergence holes per square foot in a lawn. It's a very, very dense population."

When was the last time we saw the cicadas?

The last time the 17-year cicadas emerged was in 2007. Prior to that, it was 1990.

Will there really be millions or billions of these cicadas?

"I've heard reports from 2007 and 1990 from places in Chicago area where folks would have to take a snow shovel to clear up the sidewalk," Liesch said. "So that will probably be the case in certain areas of Chicago again this spring and perhaps a few spots here in Wisconsin."

What is the experience like when the cicadas emerge?

You've probably heard cicadas during the dog days of summer. Now, imagine having thousands of them all of them at once. It creates an other-worldly sound.

"Some folks have described the experience as being kind of surreal and out-of-body," Liesch said. "Some have described it as almost a science-fiction-like experience. Just the sheer noise. I would imagine if you happen to live or be visiting one of these areas, it would be very loud. And so that potentially could even make it hard to sleep if they're making that much racket. But if you go just a short ways down the road, it might be much quieter, but it certainly can be quite an amazing natural phenomenon to experience."

Are cicadas harmful to people?

No. Cicadas do not bite or sting, and they are harmless to people and animals.

Will the cicadas be harmful to the local ecosystem?

These cicadas can be harmful to trees when they emerge. According to Liesch, when females go to lay eggs, they cut slits into the ends of twigs and insert those eggs into those slits. That can sometimes cause damage for certain trees.

For large, mature trees, Liesch said there is no concern. The tips of these trees' branches and twins might die, but the tree will be okay.

For newer, younger trees, having this large number of cicadas laying eggs all at once could be a concern, he said.

"A very simple remedy in a case like that would be to actually cover a young tree with a mesh netting to physically keep the insects off of it," Liesch said. "But for the most part, they're really pretty harmless."

Why do these cicadas only come out once every 17 years?

It's unusual in the animal world to have these long intervals.

"Most insects are generally pretty short-lived, but to have an insect that is living below ground for about 16 years and than popping out in year 17, that's definitely an unusual strategy," Liesch said.

While it isn't totally clear why these cicadas do this, it is thought to have to do with ensuring the ability of the species to reproduce and survive.

"If you are an insect and you emerge in huge numbers all at once, some of the individuals are going to get eaten," Liesch said. "But, if predators eat until they're full, there's still going to be enough to reproduce and perpetuate.

"Another thought is if you were an insect that emerged on a very regular basis, other wildlife might pick up on that. So if you had a two year or three year pattern, it's possible that some longer lived vertebrates, mammals or birds or something like that might be able to queue in on that. But if you're talking about these relatively large numbers, 13 or 17 years, that's much, much harder to predict."

Can you eat the cicadas?

Yes, and some people do in fact eat cicadas when these emergence events occur.

"I have heard of that," Liesch said. "Again, they're not harmful to people. In some cultures around the world, cicadas are included in part of human cuisine and diets. I have heard of folks doing that, but I haven't personally had the opportunity to try them myself yet."

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Drew Dawson can be reached at ddawson@jrn.com or 262-289-1324.