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This is But Why, a podcast for curious kids from Vermont Public. On this show, we take questions from curious kids all over the world and find interesting people to give us some answers. I'm Jane Lindholm and I'm... I'm Jane Lindholm and I'm... I'm Jane Lindholm and I'm the host of this show! It's getting a little loud in here. Must be all the bugs! Those are the sounds of insects known as periodical cicadas. Let's take the cicadas out for a little while.
If you live in many parts of the eastern half of the United States right now, though, you are probably very familiar with that sound, and you can't just turn the volume down like I can here in the studio. There are millions, maybe trillions of cicadas emerging across many parts of the eastern United States right now. So we thought we'd jump on the cicada bandwagon, even though we just recently did a whole other show about insects, and answer your specific cicada questions.
And the guy we're going to talk to was once a lot like some of you. I'm a little boy who loved collecting bugs and getting out into trouble outside. And now they pay me to do this at a university as a professor. And what's your official title that we would put on our actual website? Professor of Entomology at the University of Maryland. That professor is named Dan Gruner.
Entomology is the study of insects, so he's a professor who studies insects, and cicadas are one of his specialties. So what are cicadas? Well, we know they're insects, so they have six legs, three body parts, head, abdomen, and thorax, and they have wings. They don't bite, and the males are known for their loud singing, as you just heard.
Dan Gruner says cicadas don't really look like any other kind of bug. Well, they're unmistakable. And you'll have to excuse me, I'm a little bit colorblind, so I can't accurately say what the wings' colors are, except that they're brightly colored. They're like an orange to yellow color. And then their eyes are a blood red color. In most cases, there are actually a few weird ones where they might be white or blue, and people do track that.
But you can't miss them, these large black insects about an inch and a half long with these really bright red eyes. There's perhaps 10,000 species of them found on every continent except for Antarctica. Year to year what we have are annual cicadas or dog day cicadas which come out later in the year like July and August.
but it's only a few that have this really crazy adaptation where they come out only every 13 or 17 years.
The periodical cicadas, why we're hearing so much about it, is because when they come out, they come out in full billions, perhaps even trillions of individuals all emerging at once in a particular location. So most of the cicadas around the world are annual cicadas that you'll see every summer. They're still spending a few years underground, but some of them are out each year, so they're not all coming out in one giant group.
We're hearing a lot about cicadas right now because some of the 17-year cicadas and some of the 13-year cicadas are coming out at the same time right next to each other. Hi, my name is Zuzu. I'm six years old. I live in the Bronx. And my question is, why do cicadas only come out every 17 years?
Hello, my name is Vito. I'm five years old. I live in Berlin, Germany. My question is, why do cicadas only come out every 17 years? So we have four species.
in the US that come out on 13 year cycles and those are mostly found in southern states. And then there are 17 year cicadas which are in the more northern states. And we think this is very much related to climate and when you have a warmer climate that allows them more days throughout the year where they can
or they can be warm, they will speed up their cycle a little bit so that they can come out in 13 instead of 17. But that still didn't answer the question, why 17?
And we think this is because they have evolved an adaptation to avoid predators like birds and squirrels who really love to eat cicadas if they come out on all together on a weird cycle such as 17 years.
They can satiate the predators. They can overwhelm the predators. So even if they eat every cicada they possibly can, there's plenty left over to reproduce and make it into the next generation.
Like if I'm a bird who really likes to eat cicadas, and first of all, I may not even know what they are at first because I'm not used to seeing them. But then I'm getting so full eating cicadas. But if there are trillions, I can't eat trillions of cicadas. So there are still way too many cicadas to be, you know, too damaged by that predation, right?
That's absolutely correct. So there are very few birds that would have a 17-year lifespan so that they would have any memory at all of the last time they saw this incredible emergence event. And so it's all new to them. Once they figure out that they're good to eat, many birds gorge on them. But they can't possibly eat even a majority of them because there's so many.
The other reason for them taking so long is because they have a very nutritionally poor diet. My name's Anna. I'm six years old. I'm from Virginia. What do cicadas eat?
They feed on the xylem fluids in plants. That's the fluid supplied from the roots to bring water and a small amount of nutrients from the roots into the rest of the tree. And so there's not a lot of good stuff in there like sugars and amino acids and vitamins. And so it takes them a long time to develop on that resource on the roots.
You have said, and we have both said, they come out every 13 or 17 years. What does that mean, they come out? Come out from where? Good question. So they come out from underground, and for the majority of that time, they're out of sight and out of mind, feeding on the roots of trees down below the ground.
And you won't even notice that they're there until early in the spring. They start to dig out these tunnels from their position underground. And then they wait in the tunnels until it is warm enough for them to come out and that there are others coming out. So they come out with all of their buddies when it's time.
What do they look like when they're living underground? Because when we think about insects and the insect life cycle, the baby insects, when they're in a younger stage, they often look really different than the adults do.
Yes, they do. So they have five stages that they go through. All insects go through metamorphosis where they change their shape and some do it very dramatically. Like beetles and flies go through a larval stage which looks completely unlike the adult stage.
Well, cicadas are a part of a large group of insects where they have partial metamorphosis. So each time they get a little, they change a little bit and they look more and more like their adult selves. They start out as very small, very white or off-white colored insects.
first instar larvae and then they take a few years to get to the next stage where they get large enough that they're too large for their exoskeleton, which insects have instead of an internal skeleton. Once that happens, they need to shed that exoskeleton so that they can grow more to the next stage. Kieran also wanted to know, why do cicadas molt? I'm Kieran
Oakland, New Jersey. It's because they need to get bigger, so they need a bigger shell. So they have to break open the shell that they did have so they can grow a bigger one, right? Yeah, just like Superman, you know, you got to break out of that suit that you're wearing and expand yourself. And you can only do that by breaking that exoskeleton through the course of their life cycle. And they do that five times.
And for the first four stages, they don't have wings. They don't need them underground. It's only when they emerge from the ground for that final time where they come out and molt, and then they produce wings, which then harden and dry and allow them to fly. So most of their life, they're spending underground doing all of those changes and living in the dark in the
in the dirt near the roots of the tree, and then they only come out for that short time. Many students in high school are not as old as the cicadas when they come out. That's right. This year's periodical cicadas are older than probably many of you listening right now. They've been underground sipping that tree juice, the xylem, for longer than you've been alive. And now they're bursting forth and making sure everyone knows they're here.
Coming up, we're going to talk about how they make all that noise and why. This is But Why. I'm Jane Lindholm, and today we're learning about cicadas. One of the reasons we're talking about cicadas so much this year is because, as I mentioned earlier, two broods or groups of cicadas are coming out together. A 13-year group overlaps with a 17-year group about every five or six years, and they come out next to or pretty close to each other every 25-ish years.
But these two specific broods haven't come out at the same time for more than 200 years. 221 years to be specific, way back in 1803. But still, cicadas come out somewhere all the time. So why is everyone making such a big deal out of it this year?
Good question. I think cicadas are inherently exciting. If you've ever had the pleasure of experiencing one of their emergence events, it's like being on a safari. There is nature and activity and noise and all kinds of amazing things happening right there in your backyard or your park or wherever it is you witness them.
It's impossible to ignore them. They're just so abundant, but they're also, because they largely don't worry as much about predators because of this mass emergence, they're slow and easy to catch, so you can handle them and interact with them very easily. And they don't bite people. They only feed on plants, so they're harmless insects, even though some people think they look a little alien.
but they can't hurt you. So there are many reasons why they're a fascinating
They can't hurt you, but sometimes people find them pretty annoying. Dan Gruner mentioned that they come out in the millions or billions or maybe even trillions. So if you're living where there are a lot of them, you might have cicadas littering your lawn or road. Each one molts, meaning they start to get bigger than the shell they're in, so they have to split out of their shell and leave it behind. So you might have cicadas littering your lawn or road. And they're loud. Remember? I played the sound at the beginning of the show.
Sometimes it can be hard to concentrate if you're trying to do something outdoors when there are millions of male cicadas interrupting your conversation. When they're all together, they sound something like this. But an individual cicada sounds a little bit different. I asked Dan Gruner to do his best cicada impression for us. Oh dear. So there are several species. I'll give you one. And...
It's been called the pharaoh cicada, and it makes a sound kind of like pharaoh, pharaoh. And there are other species that have different songs, but that's the most recognizable and the most abundant. But now we have to imagine hundreds of thousands of your voice at the same time, right? Which is horrifying. I'd rather listen to the cicadas than my voice. Pharaoh.
When they're making their calls, how do they do that? You said they have to wait until they have their hard exoskeleton to make the sound. The males have a structure in their abdomen. Actually, their abdomen is completely hollow. So the main purpose of the males is to chorus. They have organs called tymbals that vibrate very strongly to make those distinctive calls.
And an individual cicada can be very loud in doing that. And do females make any calls, any sounds? They do not. They have a functional abdomen where they actually are in there making eggs. You know, there's organs in there and they have a different job than the males.
Those eggs, let's talk a little bit about them. Hi, my name is Tilda, and I'm six years old. I live in Sydney, and my question is how do cicadas get babies? Bye. How do cicadas get babies? Well, so when they emerge, it takes them five or seven days or so for them to completely harden their exoskeletons so that they can start chorusing.
and the males will start chorusing, producing very loud songs that can reach 100 decibels or more, because they chorus together, trying to attract females who they'll then mate with. Once they fertilize those eggs, then the females will go to these small branches and inject
the eggs into the branches. They will hatch some three weeks later and then drop to the ground as the very tiny little first instar nymphs, we call them, being the smallest larval stage. Then they'll drop down into the soil and they get down into the roots of the grasses and eventually will migrate over to the roots of larger trees.
And then that starts that whole cycle again that we were talking about. Exactly. I'm Andrew, and I'm six and a half years old, and I live in Chicago, Illinois. And my question is, why are there more cicadas at night than morning? Great question.
So once they've emerged and their population is out, then they're equally abundant during the day and the night. But when they emerge, they usually emerge at night. And we think that's because they're very vulnerable until their exoskeleton has hardened and their wings will work.
and they're very susceptible to daytime predators like squirrels and birds that can see them very easily and consume them. So if they emerge at night, then they have that window of time where predation is lower and they have a better chance of making it to the point where they can fly away.
One of the things that is also kind of neat about many different types of insects that humans for a long time have known, you can eat insects. They are a great form of protein. They are often, as you said, really abundant or there are a lot of them and so they can be a good, easy food source. With cicadas, some creative chefs have been finding interesting ways to cook with cicadas when they come out. Have you ever eaten a cicada?
Yes, I have. And they're actually just a little bit short of delicious. I don't know if that's like praise or a complaint about the taste. It is praise. It wouldn't be the first thing I would choose on the menu, but I have enjoyed them. And I've eaten them raw and they have a really nutty flavor.
And I've also had them prepared various ways. And when the right chef prepares them, then they're actually very tasty. People eat insects all over the world. Maybe they're part of your family meals. We'll actually learn a little bit more about eating insects in a special bonus episode coming out the week after this one. But back to Dan Gruner for a second. Remember how he told us at the very beginning of the episode that he loved collecting bugs as a kid?
That's one of the things he wanted to highlight for all of you. Insects are a really cool thing to study, and they're so accessible, meaning it's not hard to get to them. You don't have to have any special equipment or travel far away or learn how to scuba dive. Insects are all around us. You've got some living right near you, whether you're in the countryside or the city, the desert or the rainforest, high on a mountain peak or low on a flat plain.
So go outside and see what you can find right around you. And pay attention to the insect behavior you notice. Maybe keep a little journal with notes and questions and see if you can learn something new about an ant or a fly or your local butterflies. Let us know what you discover.
Thanks to Dan Gruner, a professor of entomology at the University of Maryland, and to Lang Elliott and Will Hirshberger for the cicada sounds. That's it for today. But Why is produced by Kiana Haskin, Melody Beaudet, and me, Jane Lindholm, at Vermont Public, and it's distributed by PRX. Our theme music is by Luke Reynolds. We'll be back next week with an all-new bonus episode. Until then, stay curious. From PRX.