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[00:00:00] Michael Hawk: Do you remember in 2021, there was big news about cicadas coming out of the ground. It was called the brood ten emergence. And it looked like brood X when spelled out, because it was a Roman numeral. Well, 20, 24, it’s going to be another year of the Cicada with the emergence of two different periodical Cicada groups or broods at the same time, roughly in late April early may. Now, throughout much of the world, cicadas serenade us in the summer afternoons, you might be familiar with that and wonder what’s the big deal about this, but in a few special locations, periodical cicadas emerge on a specific cycle every 13 or 17 years. And these emergences are like clockwork.

[00:00:39] Somehow the insects know exactly when to come out of the ground in synchrony with each other across a vast geography, but it gets better still. Multiple species of Cicada emerged together at the same time on these intervals, sometimes in massive numbers approaching 1.5 million per acre of land. And weirder still the same species might emerge on a totally different schedule

[00:01:01] offset by years and areas just a few hundred miles away. So what’s going on here? Well, this is just the start, when it comes to the amazing aspects of cicadas and today’s guest Dr. Chris Simon. Is perhaps the world’s expert on cicadas. She joined me for an incredible wide ranging discussion all the way from New Zealand. Dr.

[00:01:21] Simon has been studying cicadas for decades. She is a professor in the department of ecology and evolutionary biology at the university of Connecticut. And it has a list of accolades so long. I could spend several minutes reading them.

[00:01:32] So get ready to learn why these broods of cicadas emerge as they do, how glaciation influenced their locations.

[00:01:38] Why 13 years cicadas tend to occur further south than 17 year cicadas. And of course, how you can see them to.

[00:01:46] You can find more about Dr. Simon at cicadas.uconn.edu. And that’s spelled U C O N N for university of Connecticut.

[00:01:56] Michael Hawk: And if you’re interested in helping contribute to research on cicadas, download the Cicada safari app from apple or Google. And there’s more on that in the episode. So without further delay, Dr. Chris Simon.

[00:02:08] Dr. Simon, I am so excited to have you here today for Nature’s Archive

[00:02:13] Chris Simon: Thank you. It’s fun to be here.

[00:02:15] Michael Hawk: I’m gonna jump right in and I think we’ll meander around a little bit and hear about how you got to the position that you’re in. But I’m gonna start with how did you get interested in cicadas?

[00:02:27] Chris Simon: I was always interested in insects as a kid. I was always playing with lightning bugs and ladybugs and ants. But cicadas specifically, it was because when I was an undergraduate taking lots of biology classes, I got interested in the question of what is a species? And I went around asking my various professors and they said, oh, that’s a difficult question.

[00:02:53] so I decided that for my PhD thesis, I would study speciation. I thought if I was gonna study speciation, I needed to study something that was in the process of forming new species. I read the literature on closely related species and I found periodical cicadas. And they were ideal because they’re broken up into year classes.

[00:03:19] So each species has a whole bunch of reproductively isolated groups. And these are so recently isolated in different years that they haven’t formed new species yet, but they’re in the process of becoming species because they’re reproductively isolated. And so I decided I would study them.

[00:03:42] Michael Hawk: And I think that’s really, it’s fascinating ’cause I think for me, I don’t have an academic background in biology, but I’ve been trying to catch up. I’ve been taking classes and reading and interviewing people like yourself and you hear about, like a proximal separation where species are separated by land, by oceans.

[00:04:00] They’re island biogeography. But this is a really unique case because they’re separated by time.

[00:04:05] Chris Simon: right. It’s called Allochronic Speciation. Allochronic Separation.

[00:04:10] Michael Hawk: Are there other, cases like this, or is it mainly just cicadas that are separated in this way?

[00:04:15] Chris Simon: No, there’s a lot of periodical insects that come out in either even or odd years, and so they’re separated in time. The even populations are separated from the odd populations and there are some insects where in one species, some populations come out in the fall and others come out in the spring.

[00:04:36] Or in the past that was what caused speciation between two different species. So yeah, there’s other examples of temporal speciation.

[00:04:47] Michael Hawk: Right. And when you discovered this sort of natural experiment of speciation in progress, were you already familiar with cicadas? Did you grow up around cicadas?

[00:04:58] Chris Simon: I had seen the periodical cicadas only once, when in 1962, Brood II was at my grandmother’s house. My father pointed out these cicadas to me sitting on the tree, and he said, these insects are 17 years old. And I thought, wow, that’s weird. Where I lived on Long Island, I guess there were cicadas, but not that many.

[00:05:21] They weren’t that obvious. The periodical cicadas are on Long Island, but I didn’t live in a patch of periodical cicadas. They were farther east.

[00:05:29] Michael Hawk: that actually, that leads to a question for me. I grew up in Omaha, Nebraska, and when I look at the range maps for the periodical cicadas, they’re just barely on the edge of, maybe it’s

[00:05:43] Chris Simon: in Omaha. Yep.

[00:05:44] Michael Hawk: yeah. But I don’t remember them. I don’t know that I was aware, when I was a kid, but I know the sound of cicadas and I think those are the annual cicadas.

[00:05:54] Chris Simon: Right. Did you live there for 17 years?

[00:05:57] Michael Hawk: Uh, good question. Between Omaha and where I went to school, which was in Lincoln, which is basically down the road I was, yeah, I was there for about 18 years.

[00:06:10] Chris Simon: Uhhuh.

[00:06:11] So

[00:06:12] Michael Hawk: have seen them.

[00:06:13] Chris Simon: they were there in 1981,

[00:06:16] Michael Hawk: Okay,

[00:06:17] Chris Simon: they were there in 1998.

[00:06:19] That explains it. In 1981 I would have been too young to have any awareness, and I was gone by 1998.

[00:06:28] Oh, that’s too bad.

[00:06:30] Michael Hawk: So now here’s my ignorant question though. Are they obviously different to a lay

[00:06:36] Chris Simon: different from what?

[00:06:38] Michael Hawk: annual cicadas?

[00:06:40] Chris Simon: Ah! They’re spring cicadas and they’re small and black with red eyes. None of the annual cicadas in the United States have red eyes and there’s huge numbers of them all over. When they first come out. You can see ’em all over the trees and bushes, and then they climb up into the tops of the trees.

[00:07:02] Whereas annual cicadas in the United States typically don’t do that, although out west, a lot of the species out west do come out in large numbers some years. They’re sort of incipient, periodicity.

[00:07:16] Michael Hawk: Interesting. So yeah, I’m familiar with the scissor grinder and some of those annual cicadas. And then here I live in California now and yeah, we have different ones.

[00:07:26] Chris Simon: Yeah, the Southern California has about 40 different species of cicadas.

[00:07:31] Michael Hawk: Wow. Yeah, I had no idea. I’m constantly amazed if you aren’t studying taxa, you think, oh, it’s a lady bug, or oh, it’s name your taxa. But then you dig a little bit deeper and you find out there’s all this diversity within just that classification.

[00:07:49] Chris Simon: Right, right.

[00:07:50] Michael Hawk: Alright, I really got way ahead of myself there but I was curious about that.

[00:07:55] So it sounds like a lay person could understand it was a periodical cicada based on if they can look at it up close and they see the red eyes or the sheer numbers of them, or they read the newspaper and

[00:08:08] Chris Simon: Right.

[00:08:09] Michael Hawk: they know.

[00:08:11] Chris Simon: Nowadays it’s all over the press. The media has just exploded. So like in 1979, I think I had two interviews. One in the Wall Street Journal and one the New York Times. And that was about it. But since then, wow, it’s just increased every generation and now there’s just like several contacts a day usually.

[00:08:38] Michael Hawk: Wow. I again, feel honored that you chose to respond to mine. So we already kind of got into, the lifespan of a periodical cicada and the fact that they emerge. We didn’t talk about emergence yet, but on a periodic basis.

[00:08:55] OAre periodical, cicadas I hear a 13 year and 17 year. Can you tell me what that means and are, are there other periodicities that exist in the world somewhere?

[00:09:06] Chris Simon: Yeah. In cicadas there’s the genus, Magis cicada. It’s in the eastern United States, only east of the Great Plains, and they come out in the south, the southern part, and up the Mississippi Valley. They’re mostly thirteen-year. Then in the northeast and Midwest, and then sort of humping over the top of the thirteen-year cicadas and down the eastern edge of the great Plains all the way to Texas are seventeen-year cicadas. But we used to think that they were the only periodical cicadas, but oh, maybe in 2014 we uncovered this little newspaper, article, a little blurb that said World Cup Cicada. And it turns out that in the year of the World Cup, there’s a four-year cicada that ’cause the World Cup is apparently held every four years, I think this is for soccer or football.

[00:10:01] And so the cicadas come out in the year, like in the spring, right before the World Cup. So I found the, publications, it was published by a scientist in Northeast, India. I contacted him and it turns out that they also discovered another group that’s nearby that’s offset by two years, same species, but it’s got two broods offset by two years.

[00:10:28] And then in a book written by a cicada biologist about the South Pacific, he mentions a cicada that might be periodical in Fiji. We checked it out and sure enough, it does seem to come out once every eight years. We went to Fiji a few years ago and worked with the people there to document it.

[00:10:51] And it’ll be coming out again in 2025.

[00:10:54] Michael Hawk: It sounds like a good excuse for you to go to Fiji.

[00:10:57] Chris Simon: Yeah,

[00:10:59] Michael Hawk: So you mentioned the word brood. Can you explain in the context of cicadas what

[00:11:05] that means? ’cause I, my understanding is it’s maybe a little bit different than like a brood of birds or

[00:11:10] Chris Simon: Right. I know. It’s quite unfortunate. I can’t remember who first used that term maybe. Charles Marlott, but it’s actually just a year class. Yeah, the word year class would be much better than brood because as you said, it’s used in birds to mean that the individual’s in a nest. But it’s a group of individuals that all appear in the same year.

[00:11:34] Michael Hawk: So you picked your words carefully there, a group of individuals. So a brood could be multiple species?

[00:11:40] Chris Simon: Oh yes. In periodical cicadas, most broods have three species. There’s three different species groups; you could think of ’em as large, medium, and small species. Although the two smaller ones are almost the same size. But yes, there’s three different species. They have three different songs to attract mates and they all come out in the same year.

[00:12:04] Almost every brood. The northernmost brood only has one species, the largest one. But the other broods have all three species. Most of the other broods.

[00:12:14] Michael Hawk: Do the three different species tend to emerge around the same time of the year?

[00:12:20] Chris Simon: Yes, they merge very close together in time, although the two smaller ones seem to be a little bit later than the larger one. But that’s because they have this safety in numbers strategy for survival.

[00:12:34] Michael Hawk: Right. I love these conversations because there are so many branching points and so many different directions that we could take it.

[00:12:41] Chris Simon: That’s good. Yeah. It’s very hard to even write about them because you have to explain the whole thing in every paper.

[00:12:48] Michael Hawk: right, right. And somebody unfamiliar with cicadas, I think when I first heard about them, I just assumed a brood was a single species. Then you get into this, next layer of complexity and as we’ll talk about today, and as you shared with me offline, there’s even more layers of complexity in this

[00:13:07] Chris Simon: Oh yeah

[00:13:07] Michael Hawk: As well. how many North America anyway, how many broods do you track?

[00:13:14] Chris Simon: Okay. There’s 12 existing broods of seventeen-year cicadas, but there could be 17, right? Because there’s 17 different years between when one comes out and comes out again. But there’s only 12 that we know of. There was the 13th one, but it went extinct. It was in Connecticut and it went extinct in the 1950s.

[00:13:35] Then in the thirteen-year cicadas, there could be 13 different broods, but there’s only three that are well documented, well developed. And as I said, they’re mostly in the south and then they come up the Mississippi Valley.

[00:13:49] Michael Hawk: you’ve already started to describe a couple scenarios, not just in North America, but also these uh, you know, like the World Cup cicada, for example, where this number of, four seems to be prevalent. The difference between 13 and 17 is four and so on. And as I understand it, and we’ll talk a little bit more about how or why or what the hypotheses are here in a moment.

[00:14:13] But as I understand it, sometimes individuals in the brood, their timing gets off a little bit.

[00:14:19] Chris Simon: Right. Sometimes, a large number of individuals will come out four years early or sometimes four years late, and that even happens in seventeen-year cicadas, and in 13 year cicadas. In thirteen-year cicadas, if you go to a place that you know is gonna be really dense and you go there four years ahead of time, there’ll be quite a few cicadas coming out.

[00:14:42] And the same for seventeen-year cicadas; if you know of a place that in the historical records, it’s very dense, and you go there four years early, you’ll see a large number of individuals coming out. It seems to be increasing the number of individuals that come out early, in seventeen-year cicadas at least, seems to be increasing over time because the first record in the literature of this happening, the biologists from the University of Chicago and Field Museum went out to check it out and they said, yeah, that there was thousands of them. They collected all the shells, but they disappeared in a few days eaten by birds and other predators, and they did not hear any singing.

[00:15:28] So right now we’re coming up to that same brood that’s gonna be coming out brood 13 in Chicago area and throughout Northern Illinois and into Iowa. And four years ago, a whole bunch of them came out in large numbers and they were out for the entire four weeks. They were singing and they successfully laid eggs. And the same thing happened in Washington DC with Brood 10, which came out in 2021. Four years before that, in 2017, there were huge numbers in the DC area but they stayed out the entire time. It sounded like a normal brood. And they laid eggs and the eggs hatched. And so it seems like there’s gonna be the start of a new brood that’s four years earlier than brood 10.

[00:16:20] Michael Hawk: That’s, again, fascinating to think about what’s going on there and what the implications might be.

[00:16:26] And you know, that these are members. Early members or late members in the other case of the given brood? Because of the location they’re at? Or is there some, are you doing some DNA analysis or like, how do you know that association?

[00:16:41] Chris Simon: Yeah. Unfortunately we can’t tell the broods apart, even by the DNA. All that we can tell by looking at the DNA is that all the broods are divided into eastern US, east of the Appalachians, Midwest, west of the Appalachians, up to the Mississippi Valley, and then Western is along the eastern edge of the great Plains South, that’s the western group. So all of the species and all the broods show this geographic pattern that’s a remnant of the ice ages where they got forced down during the ice ages. All the forests were forced down along the Gulf Coastal plain, along the Blufflands of the Mississippi and the coves of the Appalachians and in the Ozark Mountains there were little pockets. Then as the climate warmed, the trees moved north and the cicadas moved slowly with them. This is like over thousands of years . So by 10,000 years ago, the trees were pretty much back to where they are now. And the cicadas moved north slowly with the trees. And the brood formation must have taken place after that because the ice was there before, so they couldn’t have been there before.

[00:17:53] Michael Hawk: So in the relatively short period of time where we have records of these cicadas do you see changes in their ranges occurring?

[00:18:03] Chris Simon: Yeah, because of human development. When you tear down the trees and you build parking lots and things like that, the cicadas are killed. But luckily in a lot of areas, the development has been sort of mosaic, where you have patches of forests cut down to make fields, and then the fields were abandoned. Like in the Washington DC area, the cicadas are doing very well in the suburbs, all around DC and Baltimore.

[00:18:34] Even though that’s a really heavily settled area, there were fields at one time, and those fields were abandoned, but they left. The fields were surrounded by forest patches and especially along rivers and streams and creeks. And then housing developments were built in the fields and people planted trees in their yard.

[00:18:55] And the cicadas like edges, the females like to lay eggs in edges and they particularly like small trees because they’re rapidly growing and they’re gonna be there at least for 17 years. So the natural selection has favored female cicadas that lay their eggs in younger trees, in brightly lit areas that are gonna be growing faster.

[00:19:17] So the suburbs is just filled with periodical cicadas there because the suburbs now is full of big trees.

[00:19:25] Michael Hawk: Yeah that’s also really interesting so let’s talk about habitat requirements then a little bit.

[00:19:29] You mentioned that they seem to prefer the younger trees and a couple of reasons why that might be. Are there specific species of trees that they prefer over others? Are there any other kind of micro habitat or specific habitat requirements that they have?

[00:19:46] Chris Simon: They’re generalist species and they generally don’t have preferences. That was studied by Joanne White, who, at the University of Chicago with her major advisor, Monty Lloyd, who’d been studying periodical cicadas for a long time, they looked at oviposition preferences, where they lay their eggs, and they looked at all three species and Joanne learned to be able to tell apart the species by what their egg nests looked like.

[00:20:12] So they recorded that and they did not find any particular preferences. They did find that there were trees that they seemed to avoid. They wouldn’t lay eggs in Osage orange because it was too hard. Wood was too hard. But mostly they laid eggs in everything. However, of the three species of periodical cicadas, one of them has a habitat preference for floodplains.

[00:20:38] So that’s the sort of intermediate size black one called Cassani group. It’s in the Cassani group. And so those live in floodplains so they’re mostly in trees. They lay their eggs mostly in trees that live in floodplains. And there are some trees are more common in floodplains and some trees are more common in uplands.

[00:20:59] But they’re generalists. They don’t lay eggs in pine trees. And they don’t emerge in sort of solid pine forest. But if there’s any kind of understory with woody plants that could support cicadas. Yeah, they’re generalists.

[00:21:16] Michael Hawk: So that’s interesting to then pick apart when, it was determined that this, the intermediate species is found in the flood plains, seeing that it is multiple trees or still generalists there.

[00:21:27] Chris Simon: Oh, but they will occur in the uplands too. So especially in disturbed habitats, you can find all three species side by side in the same place. So they’re not absolutely restricted to the floodplains, but they’re just much more common. And in fact, when I was talking to some biologists living in Missouri, and we were talking about the most common species, they were talking about the middle-sized one, and I was talking about the big one because in the East coast and in the north, the bigger one is the more common species.

[00:22:00] But in the floodplains of the Mississippi River drainage, the small black one is the most common species.

[00:22:08] Michael Hawk: Is there any kind of direct competition between the three species when they’re all emerging at the same time?

[00:22:15] Chris Simon: When laying eggs, there’s always competition for space. I guess underground also there would be competition for rootlets. So yes, there would be competition between the different species. The slight differences in size I don’t think would make that much of a difference to the nymphs in the habitat partitioning.

[00:22:36] They go through five stages. Having this long life cycle makes less competition among the five different stages because they’re separated out in time more. So in the beginning they’re mostly all small, and then you start getting bigger ones bigger and then larger ones and larger ones.

[00:22:54] Chris Simon: But the really interesting thing about periodical cicadas is that even though all the species in a particular area, all three species and all the individuals emerge within a period of about a week they don’t grow at the same rate underground. So even though they have an exact length life cycle, they’re growing at all different rates underground. So some have to catch up or else just not be ready to come out. And if they’re not ready to come out, they’ll keep growing for another four years and they’ll come out. So they have these windows of four years, once they get to the last stage and they’re big enough, they’ve gone through all the changes necessary, they can come out, but they only do it in these windows of four years.

[00:23:38] Michael Hawk: That’s really interesting too because the analogy that came to my head there is if you’re on the subway and you miss your stop it’s kind of like, for them, if they aren’t ready, it’s oh, four years more. I missed my stop.

[00:23:53] Chris Simon: Yep.

[00:23:54] Michael Hawk: Why don’t we tie up the loose ends on the life cycle piece.

[00:23:58] In the course of this discussion, we’ve already talked about different elements of it. If you could walk me through the life cycle. If there’s a difference between 13 and 17 years ? We go ahead and cover that, but just what generically kind of, what does it look like?

[00:24:11] Chris Simon: Periodical, cicadas come out in the spring. They emerge from the ground. And they’ve spent either 13 or 17 years underground growing up. But they emerge within just a few days of each other. So the first week of an emergence will be mostly, you’ll see cicadas all over the trees and lower down in the vegetation, and then they’ll start crawling up into the tops of the trees.

[00:24:37] The second week of the emergence, the males will start singing. And if you actually look at the individuals, the males come out slightly before the females. And this happens in a lot of insects, ’cause apparently the males by natural selection are more expendable. And they’re very close together.

[00:24:53] Just a maybe a few days. In the beginning there’ll be mostly males. And then in the middle of the emergence week, there’ll be both sexes. And then near the end of the emergence week, it’ll be mostly females, but it takes ’em a while before they can start singing.

[00:25:09] So they start singing. After about a week, only the males sing, not the females. And then during the end of the second week and the beginning of the third week, they start mating. And then during the third and fourth weeks, they start laying eggs . They lay eggs and the males tend to die before the females.

[00:25:27] So near the very tail end of the emergence, it’ll be heavily female biased. That’s because the males come up a little bit earlier, so just a few days earlier. Also the males are singing, and so predators can cue in on the males, whereas the females don’t sing. But they do make a little quiet wing flick to the males.

[00:25:48] When the males are calling the females who coming close then make the wing flick and then they’ll orient towards each other and then they’ll mate. So then after the females lay the eggs, they’re in the branches for about six weeks. And so the eggs hatch later in the summer. And all of the nymphs will just launch themselves into the air out of the tree branches.

[00:26:11] Oh, and the eggs are laid in, slits in the tree, branches in v-shaped nests, and each nest has about 12 eggs. Then they go down the branch it looks sort of like a sewing machine has gone down the branch and they lay a whole bunch of these v-shaped nests, and then they’ll make another nest.

[00:26:29] And so they’ll just keep, they’ll make a skip and then start another nest. And if they’re disturbed, they might fly to a different branch and make nests and, so those eggs hatch, the eggs fall to the ground as a first stage nymph, we call instar. The stages are called instars in insects. And so the first instar, nymph is the shortest.

[00:26:51] It lasts for about a year or less. And then the second stage, third stage, fourth and fifth, all have an average length of about four years. But as I said, they all grow at different rates. Some will be bigger than others and the laggers fall farther and farther behind as you go through the life cycle.

[00:27:11] So there’s much more of a spread in the nymphs as you get older. So say if you dug up a population of 17-year cicadas at nine years, you might find some second instars, some third and some fourth, or you might find some third, some fourth and some fifth. All together in the same population.

[00:27:33] Michael Hawk: I think we can infer a couple answers, like tying together with some things you said before. So the females lay their eggs in these little v slits and they’re choosing softer, newer growth it sounds like.

[00:27:47] Chris Simon: Yes, but not the newest because that’s too soft. So it’s one node back from the newest growth. Yeah, and they’ll lay eggs in there. We say pencil-sized branches. But the two smaller species, I’ve seen them lay eggs in Blackberry poison ivy. Queen Anne’s lace even, but that’s not the typical place that they lay eggs.

[00:28:11] Michael Hawk: And when the instars, when the first instar emerges and they go to the ground, are they then just burrowing straight into the ground to find roots to feed on?

[00:28:22] Chris Simon: Yeah. They’re very tiny and so , some people have described it as they’re sort of searching around for little cracks in the ground, but they do burrow down in, they dig down in, and at the beginning they might just stay up, like if they’re on the edge of a park or something, they might just stay up in the roots, or if they’re in the forest, they might just not be that far below the leaf litter as a first instar.

[00:28:48] But then as the weather gets colder, I suspect they probably go a little bit deeper in the ground, work their way down. But they’re tiny, so they’re feeding on tiny rootlets. And then, for the rest of their life, they’re generally between, about, at least in the spring when you could dig or in the fall, before the ground freezes, they’re generally anywhere from say seven inches to a foot down. That’s where most of them are.

[00:29:15] Michael Hawk: So do they actually then go deeper when the ground’s frozen?

[00:29:18] Chris Simon: Yeah, we don’t know because we can’t dig ’em up when the ground freezes, although I guess we could get some machinery in there.

[00:29:25] Michael Hawk: yeah. You mentioned too that it takes them a while to start singing, when they emerge as adults. Are they still developing at that stage?

[00:29:36] Chris Simon: yeah, when they first come out, the chitin is still a little bit soft, especially on the inside. They generally come out in the evening and they’re white. Then they unfold their wings and they pump fluid through.

[00:29:52] They stretch them out, and then overnight they harden. And as they harden, they turn darker color. And so by morning they’re often black. But if there’s a very dense population, they’ll come out night and day, they’ll just keep coming out. In a normal population, they come out in the evening, they turn black overnight.

[00:30:11] But if you turn ’em over and you look at the underside, you can see that the male and female genitalia are still like light brown colored, not black. And or even whitish. So they’re still very soft. It’s called tenoral. I assume that the places that the muscles attach inside are also still a little bit soft, and so it takes them a while, but this is only true of periodical cicadas.

[00:30:39] So in New Zealand, I’m studying these cicadas that live in our backyard in Wellington. The females and males will mate the same morning, the morning after they come out of the ground so they can mate immediately. And then it takes a few days before the females will start laying eggs.

[00:30:57] But that’s completely different from periodical cicadas, which they seem to do everything slower.

[00:31:04] Michael Hawk: Do the periodical cicadas tend to average to be larger in size than other cicadas?

[00:31:10] Chris Simon: No. No, the annual cicadas are bigger, wider and some of the annual cicadas are much bigger. They’re sort of medium-sized cicadas. There’s some very tiny little cicadas, say for example, we know of some in Australia that are maybe the size of your fingernail. And then there’s some very large cicadas also in Australia and new Guinea, tropical areas.

[00:31:36] Michael Hawk: I when you said very large, I could see your hands was that really how big they get? I, maybe you can

[00:31:41] Chris Simon: describe biggest

[00:31:41] oh, yeah.

[00:31:42] Michael Hawk: ones.

[00:31:43] Chris Simon: Yeah. I didn’t look up the exact measurements, but I would guess maybe six inches long, something like

[00:31:49] Michael Hawk: I can’t even imagine that

[00:31:50] Chris Simon: They’re very, They’re really big. Yeah, they’re really big. And they can be heard from long distances. There’s one in New Guinea that’s called the ‘Quittin time’ Cicada, because it sings at night a really loud burst for just a short time, but every evening right about the time you’d quit work.

[00:32:10] Michael Hawk: I love it. So many evocative names in the insect

[00:32:14] Chris Simon: world

[00:32:14] yeah.

[00:32:14] Michael Hawk: I had the great fortune. I know we’re off track from periodical, cicadas here for a moment, but I had the great fortune to travel to Australia a few times and one of the years I was, there was a really good year for the, it’s a common cicada called the Green Grocer.

[00:32:30] And uh, and I mentioned the scissor grinder earlier as well. There’s so many great names.

[00:32:37] Chris Simon: And they have the flowery baker, the cherry nose. And they even, you can buy candy in a bag. That candy has all the different flavors of four different cicada flavors.

[00:32:49] Michael Hawk: Wow. Where do you buy this? Australia?

[00:32:52] Chris Simon: In Australia.

[00:32:54] Michael Hawk: I missed that. Next time if I get the chance to go back I’ll look. So I wanna get back to their songs here in a little bit, but before we do that can you tell me what’s all the fervor about 2024. What makes 2024 so special?

[00:33:08] Chris Simon: It’s because two broods are coming out at the same time. A thirteen-year brood and a seventeen-year brood. That happens roughly every twenty-five years. But most of them don’t come near each other. Maybe it’s every five years that you can find a 13 and a 17 coming out in the same year.

[00:33:28] But most of them are not near each other. This is nice because they’re very close to each other, but we don’t know of any place for sure that they’re in the exact same trees. We’ve mapped these broods individually before. Illinois is one of the best mapped places; they were mapped there even before I started working on them, and and they continued to be mapped by other people.

[00:33:56] Including some of my former post-docs who did a lot of mapping there. From all of our maps and all of our data, we don’t know for sure any place where they’re actually touching each other. They come really close. There could be some patches, but nobody will be able to tell because where they come out together this year, they’ll appear and sound identical.

[00:34:18] Michael Hawk: So when you say they come close, based on these past mapping exercises, how close do they come?

[00:34:25] Chris Simon: Oh, maybe less than a mile from each other. Around Springfield, they’re fairly close together. So there’s a number of different places, but we don’t know of any place for certain that they actually overlap in the same trees.

[00:34:40] Michael Hawk: Is there any idea as to how far a male or a female might disperse from where they emerge?

[00:34:48] Chris Simon: Yeah, that they generally don’t disperse, but they can fly. Cicadas in general, even though they fly, are pretty sedentary. Not even, not just periodical cicadas, but all cicadas. They don’t undergo these big migrations. They tend to fly around. And if you study a whole patch of forest, which has been done by other ecologists, have studied a big patch of forest in Arkansas.

[00:35:13] And you can see that over time the favorite trees for male chorusing will change over time in the forest. So just one down they’re still fairly close to each other, but they don’t go somewhere else in large groups; they don’t fly in large groups somewhere else unless a storm picks them up or something like that.

[00:35:34] Michael Hawk: So do you expect, I’m gonna get back to what makes 2024 special, but do you expect with this like co-emergence occurring then that there will be gene flow between the broods?

[00:35:45] Chris Simon: There could be. If they do come out in the same trees . They’ll sound alike to each other. So there could be, but we don’t know if there will be. It’s much more likely that you get gene flow between two seventeen-year broods that overlap. ’cause in seventeen-year cicadas, there are broods that we know occur in exactly the same trees.

[00:36:08] Michael Hawk: Okay.

[00:36:09] Chris Simon: But if that happens, we know that they’re always at least four years apart. They never co-occur in the same trees if they’re less than four years apart. But that means that if they come out four years early, they’ll join the other brood. And that’s one of the reasons you can’t tell the broods apart by the DNA because they move through time from one brood into another by these four-year changes. Oh, and by the way, Omaha is one of the places that we know of a four-year late group of cicadas. There’s a park just north of the city. I forget the name of it. Do you remember?

[00:36:43] Michael Hawk: Could it be Neil Woods?

[00:36:46] Chris Simon: No, that’s not it. Anyway, there’s a park just north of the city of Omaha where they came out four years late, in 1985 I think it was, , but it didn’t happen again the last time Brood IV came out in 2015. We waited for 2019 and we contacted the people who work in the park, but they didn’t see another emergence four years late.

[00:37:09] Michael Hawk: Interesting. From a biological standpoint, from a natural history standpoint it’s exciting to have this co-emergence with the overlapping from a regular person’s point of view. Are they going to notice more cicadas because of this?

[00:37:24] Chris Simon: No, it should just be the same densities as normal. But you have to remember that the density can fluctuate quite a bit from one population to another. And also in a single population, it can change over generations. Some generations there’ll be a lot more than others. And when you, drive around mapping them, people will say, oh, there aren’t so many this year as there were the last time they came out, and things like that.

[00:37:52] Or there’s a lot more this time than the last time they came out. An ecologist Rick Karban from Davis has actually studied that, he’s gone to the same populations. Three generations in a row and shown that some can go up, some can go down the same year, one population will get more dense, another population will get less dense.

[00:38:14] So it varies over time and across geography.

[00:38:18] Michael Hawk: Let’s talk a little bit about the enormity of like a good year. I’ve seen some really surprisingly large estimates and it, it’s gotta be just really hard to do these estimates, I would imagine to,

[00:38:29] Can you help me or help the listeners and me wrap our heads around the enormity of some of these emergence.

[00:38:37] Chris Simon: Yeah. The densest population ever recorded was in Raccoon Grove in Illinois. In 1956 I think it was a million and a half per acre. And that was the small black ones in the floodplains. So they recorded a million and a half per acre, and in their paper, they recorded the previous studies by other researchers.

[00:39:00] The river floodplain populations were more dense. And somebody else , recorded A million three hundred thousand per acre, others just a million. But then in the uplands, it’s more like in the hundreds of thousands per acre. So that’s spread out over an acre.

[00:39:16] But in the really dense areas, it’s incredibly loud, especially when all three species are there. Although the smaller two are much louder and much more annoying, the largest one. The Decim group, they have a nice calm whistle sound and it sounds like flying saucers from a 1950 science fiction film.

[00:39:38] If you go into an area and you ask people if they’ve heard anything, it sounds like a flying saucer. And the cicadas are there. They’ll, the Decim ones, they’ll say yes. So it really does sound like flying saucers.

[00:39:52] Michael Hawk: Let’s talk about their songs a little bit more. ’cause I don’t know how much of this is myth, how much is reality? You have three species all singing at the same time.

[00:40:11] Let me pause this train of thought actually for a second at this time of year, because you said that they emerge in May-ish, if I heard you correctly.

[00:40:19] Chris Simon: If you’re in the Baton, Rouge Louisiana, they’ll be out in April,

[00:40:25] in mid-April. The earliest annual cicadas might come in near the end of the periodical cicada emergence. So you do get a few, not very many other one species may be singing, but most of the annual cicadas are at the late summer.

[00:40:43] Michael Hawk: Yeah. Okay. So now, back to the periodical, cicadas, they don’t have a lot of interference then from the annuals. But I’ve heard that there’s an element of synchrony that happens in their songs when the males are singing.

[00:40:57] Chris Simon: Yeah, for, especially for the medium-sized species, Cassini. the The Cassini group, when they really get going, yeah, they tend to synchronize and they’ll just the chorus will just swell all together. But their song has two parts. it’s like a bunch of ticks in the beginning, almost sounding like a ratchety sound like tick tick, tick again.

[00:41:19] Then a big loud screechy buzz. And there’s loud screechy buzz will just when they’re chorusing together and they become synchronized, it’ll just up and be super loud Then it’ll die down and then they’ll do it again. And, but the Decim they don’t do that so much. They might synchronize a little bit, but mostly not so much.

[00:41:49] And the Decula, but the Decula do they, they synchronize too. So they’re just more chsee-chsee-chsee like a little tambourine and they will get to be synchronized in the end.

[00:42:01]

[00:42:15] Michael Hawk: Are there any rationals or hypotheses as to why they synchronize, the ones that do?

[00:42:22] Chris Simon: Could be natural selection for a great big, giant mating display and the loud noises could also maybe confuse predators.

[00:42:32] Michael Hawk: Yeah. You wouldn’t know where to look. I guess it’s just like it’s coming from everywhere.

[00:42:36] Chris Simon: Yeah. And also very annoying.

[00:42:41] Michael Hawk: Yeah. For anyone in this area who’s starting to anticipate some sleepless nights due to the cicadas, about, about how long in a given night do they sing all night, and how

[00:42:51] long of a

[00:42:52] Chris Simon: period?

[00:42:52] They don’t, yeah. Generally cicadas sing in the daytime, however, if there’s huge numbers and it’s really warm and something wakes them up, they will start to sing at night. Like I’ve been camping underneath them. Everything’s quiet and then all of a sudden you hear one make a little squawk and then they all start squawking together and then all of a sudden you got this chorus going, but then it dies back down again ’cause it’s nighttime.

[00:43:21] So they will occasionally sing in the night, but they don’t normally sing at night. So if people tell you that these things have kept them awake all night, they’re probably not talking about periodical cicadas.

[00:43:35] Michael Hawk: Yeah. Maybe

[00:43:35] it’s a cricket or a Katydid

[00:43:37] Chris Simon: A Katydid. Yeah,

[00:43:39] something like that. And then, but in early in the morning, I’ve also been camping out in an area that was mostly the large species, Decim.

[00:43:48] Early in the morning you start hearing this quiet whistling sound and they’ll just sort of sit there and hum early in the morning. But then they’ll close down and then when it starts getting more sunny, they’ll start singing more loudly. And there are like the smaller two species, Cassini and Decula, they usually don’t start singing till about 10 o’clock in the morning.

[00:44:11] So there is some division of the airspace There’s often sort of in the middle of the day when it’s super hot, it’s more quiet. then once it cools down a little bit, then they’ll start loud choruses again in the late afternoon. All the species. So it varies throughout the day. It depends, if it’s raining, you might not hear them at all.

[00:44:33] Michael Hawk: And something I meant to ask a little bit earlier when we were talking about life cycle as adults, are they feeding at all or is it just like they’re there to reproduce? They are

[00:44:44] Chris Simon: Oh, they definitely feed as adults. In fact, if you walk under a tree full of adults, you’ll feel water droplets coming down. It’s like rain. And in fact if you go to Singapore, a tourist attraction is called cicada rain. And you can walk through forests on these tours and get rained on with cicadas who are expelling fluid they feed on watery xylem fluid, and then they eject what’s left over out the rear ends and it falls out as cicada rain.

[00:45:17] Michael Hawk: Would you consider that I know Aphids, for example, will excrete Honey Dew you know, sweet. Is it similar? Is it kind of like a sweet

[00:45:26] Chris Simon: Yeah. It’s similar. No, it’s not. It’s not sweet. However, in Africa, there’s one species of cicada that I think does excrete sweet liquid, which is really strange. But online, there’s a video called the Queen of Trees. In the video they focus in on a giant fig tree and all the life of that tree, they show cicadas, expelling liquid, and the liquid falls on the leaves of the tree, and then monkeys come and lick it off.

[00:45:56] And so I, I wrote to the filmmaker and I asked him if he tasted the leaves, and he said yes. And he said they’re sweet.

[00:46:05] Michael Hawk: Wow.

[00:46:05] Chris Simon: liquid is sweet. I know that there’s at least one cicada that has a sweet exudate, but majority of cicadas not so much. Although when you think of it, maple syrup is actually xylem fluid coming up from the roots in the spring, and so that’s sweet but you know, very dilute. So Xylem will have some sugars in it, but generally not as much as that African one.

[00:46:31] Michael Hawk: Where I, my head was going with this is, anyone who’s listening to this podcast knows that I actually, I love aphids. I think they’re really interesting. And and then watching the interaction with the ants when they realize that there’s this free food that the aphids are creating for them.

[00:46:48] Is there any I guess we have the monkeys in Africa, but in the periodical, cicadas, are there any other insects or anybody taking advantage of this excretion from the

[00:46:59] Chris Simon: cicadas

[00:47:00] Not that we, yeah, not that we know of. Not that we know of. But yeah, it’s not just aphids, it’s other, so those guys are feeding on phloem, aphids, mealybugs, scale insects, and ants actually you farm them. They pick up the mealybugs and the scale insects. They carry them onto your plants and they start these farms.

[00:47:23] In fact, in Hawaii, it’s really hard to keep any hibiscus alive because the ants are constantly carrying mealybugs onto them and farming them.

[00:47:33] Michael Hawk: And I guess you said not