17-Year Cicadas Primed To Emerge

This spring the massive "Brood II" batch of 17-year cicadas is expected to emerge from the ground in backyards and parks all along the Eastern U.S. The insects will mate, lay eggs, and start the cycle all over again. Cicada expert John Cooley explains the unusual biology and evolution of periodical cicadas.

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IRA FLATOW, HOST:

Up next, ready for an insect invasion?

(SOUNDBITE OF CICADAS)

FLATOW: Wow, almost had to turn down the sound on that one. If you live on the East Coast, you might remember a similar sound from back in 1996. That's the last time we heard from Brood II, the mass millions of cicadas that crawl out of the ground every 17 years. And they are scheduled to make a return appearance this spring, singing that love song in backyards and parks from Atlanta to Hartford.

The cicadas will mate, they'll lay eggs and die, leaving the next generation to crawl back underground until it's time to do it all over again in 2030. Are you ready for them? Joining me now to talk about this periodical cicada is John Cooley, research scientist at University of Connecticut in Storrs. Welcome back to SCIENCE FRIDAY.

JOHN COOLEY: Thank you, and good afternoon.

FLATOW: Good afternoon. Why do they make this recurring appearance?

COOLEY: Well, you know, that kind of is the real question. They are unique among cicadas in that they combine this mass emergence and this periodicity - they're all out at the same time - and this strange prime-numbered life cycle. And in all honesty, we don't have a great answer for that yet. Every hypothesis we come up with is still missing something.

FLATOW: How do they all know to come out at the same time?

COOLEY: Well, the current understanding is they're sitting there and they're counting the annual cycles of the trees or whatever they're feeding on underground. They feed on roots. And these plants go through the yearly cycle and somehow the cicadas can count that.

FLATOW: So they're not dormant, they're actually alive and eating the roots of the plants?

COOLEY: Oh yeah, they're down there doing whatever they do underground, growing and - you know, they start out very tiny, and they grow to be quite large. So they're doing something in that 17 years.

FLATOW: Tell us about this Brood II. What does that mean, Brood II?

COOLEY: Well, you know, once people started looking into these cicadas and keeping track of them, they realized that different regions seem to be on different emergence schedules. And they termed those regions that all emerged on the same schedule broods. And so this is Brood II, last year was Brood I, next year will be Brood III.

And the different broods, if you make maps of them, they all fit together a little bit like puzzle pieces.

FLATOW: So why does the 17-year one get such attention?

COOLEY: Well, you know, actually it's kind of interesting. This brood, Brood II, gets a lot of attention because it involves the New York metro area. It's not the largest brood by any means, but it happens to hit New York, and so it's getting a lot of attention.

FLATOW: That Broadway attention.

COOLEY: Yeah, exactly.

(LAUGHTER)

COOLEY: Bright lights, big city and cicadas.

(LAUGHTER)

FLATOW: OK, now, how do you know - I mean you're going to hear them when they're finally out. Do they come out in, you know, slightly, gently, or are they all out at once, one night they're there, and one night they're not there?

COOLEY: Gently, that's...

(LAUGHTER)

COOLEY: I'm not sure this is a gentle sort of thing.

(LAUGHTER)

COOLEY: No, they - you know, when they're out as adults, you really have cicadas. It's not something you can ignore. At the same time, you know, the actual emergence of the nymphs from the ground, that's going to depend upon the weather. And I have seen emergences where there is one or two nights, and it's just utterly unbelievable, these things coming out of the ground and crawling up the trees.

You can hear them walking, it makes so much noise. And I've seen other years where it was rainy and cold and horrible and it just went on forever. Once they're out and they're active, it'll be unmistakable.

FLATOW: Yeah, but so they'll come out gradually, a few thousand at a time, until there's masses of millions of them?

COOLEY: Well, you know, depending again on the weather, if we have a spring that keeps going strange and cold like this, it's going to take it a while to really get going. But they - and they accumulate as they come out. It might drag out over a week or so, the emergence from the ground.

And then once the adults are out, they stick around for about a month. And so you do accumulate large numbers of them.

FLATOW: Yeah, and so there are more cicadas, different kinds of cicadas, different species of cicadas.

COOLEY: Oh yeah, I would say worldwide there might be 5,000 or 6,000 species of cicadas. But here we have, you know, seven species of periodical cicadas, and only three of them are in Brood II.

FLATOW: 1-800-989-8255. Let's go to Wichita. Hi Gary, welcome to SCIENCE FRIDAY.

GARY: I think you answered my question because when I was talking to the screener, I asked, you know, what's the difference? I hear them every year. But it sounds like there are some that come every year and then some that come every 17 years.

COOLEY: Yeah, that's right. That's very good. We do have what we call dog-day cicadas, the sounds of summer, and they show up in July or August, at least around here, a little earlier where you are. And we have them every year. We don't actually know what their life cycles are like because it's hard to work out. They could be just as long, and we don't know it.

FLATOW: Gary, have you seen any this year yet?

GARY: Not yet, and I have been working out in the yard. But I have a great story from when I was a kid in the '80s that I remember to this day. In our neighborhood, kids were always outside back then, and one nymph started climbing up a light pole, a street light pole, and it was a blonde pole, so you could see it, and strangely enough the kids didn't bother it.

And we watched it go all the way up to the pole throughout the day until eventually I guess it molts or whatever as it's climbing up a tree or whatever, and then it took off eventually. But I guess that's part of the cycle; they come out and they climb something until they're ready to fly away?

COOLEY: Yeah, they climb something and undergo their last molt, and then they're in the adult form, and then they harden up and are ready to go.

FLATOW: Good luck seeing them this year, Gary. Thanks for calling. Well, he's out in Wichita. He's not going to see this...

COOLEY: He's going to have to wait two years to Brood IV.

FLATOW: Brood IV. We're in Brood II, from stretching the whole East Coast or just...

COOLEY: Well, you know, that's a good question. We - one of our big goals this year is to figure out exactly where Brood II is. We're working on some - working with some very old maps, and we'd like to update them. We have records from the northeast corner of Georgia all the way up the Hudson Valley in New York. I think it's going to be a little more restricted than that, but we'll see.

FLATOW: Should people be fearful of them?

COOLEY: You know, they always are, but they shouldn't. These are harmless insects. They're very friendly insects, actually, fun to play around with and watch, and they really can't do you any harm.

FLATOW: Now, I've heard that people actually eat them, fry them up...

COOLEY: Indeed, that's one of those things that comes up every time we have a big emergence, and there'll be any number of newspaper articles and recipes and all that. I mean it is an insect. It's probably not - well, it's not all that different from cooking up shrimp, say. And so you'll see a lot of recipes about that. And I think people eat the nymphs or the newly emerged adults. They don't like to eat the hard adults because it's kind of crunchy.

FLATOW: Crunchy, yeah.

COOLEY: The flipside of that is I always feel kind of bad about that because, you know, I think there's an element of conservation about these cicadas, and they're a little bit more like passenger pigeons than we might like to think. And their populations in some areas might be in trouble.

FLATOW: Is that right?

COOLEY: Yeah, I think that's probably the case. And there's another dimension to that, and that is that there's a little body of literature about mercury bioaccumulation in these things. I sit back and think about that, and maybe I don't want to eat them. I don't know.

FLATOW: Yeah, yeah. That's interesting. Why are there so many at once? What is there about nature that wants to put a million of them out there at once?

COOLEY: Well, the - you know, the hypotheses for that all seem to involve predators. And these cicadas have a really unusual strategy for dealing with predators. If you look at our dog-day cicadas, our summer cicadas, they're very hard to catch as adults. They have very good eyesight, they're very fast fliers, they see you coming, and they're gone.

These cicadas, you can collect them with a shopping bag and a pair of winter gloves. They don't try to get away. And that's because they have safety in numbers. So these large numbers, these insane densities, you know, millions per acre, all that seems to be tied together with this periodicity and this problem of avoiding predators, and it's just part of their strategy for not being eaten up by the birds.

FLATOW: Birds can't eat them all.

COOLEY: No, they can't - birds can eat as much and as fast as they want, and it doesn't make a dent.

FLATOW: Wow, let's go to the phones. Jeremy in Tampa. Hi, Jeremy.

JEREMY: Hello, how are you?

FLATOW: Hi there.

JEREMY: I wanted to call in with an interesting comment. I'm a carpenter in Tampa, Florida. I work on old homes. And I have the table saw out very often. And I will get attacked by these things when the motor runs. I believe they mistake it for their mating call.

COOLEY: Yeah, that's a neat point. These are acoustical insects, and they really are keyed into sound. And those of you in the Brood II emergence area, if you go out there with a weed whacker or something like that at the height of the emergence, you might find yourself attracting cicadas because they're coming to that sound.

FLATOW: Wow.

JEREMY: Yeah, they kind of hurt too.

(LAUGHTER)

FLATOW: Do they hop on you, they hit you as they fly? What's going on there, Jeremy? Describe it for us.

JEREMY: Yeah, I mean it seems like just a direct shot out of nowhere, maybe like getting hit with a, you know, a full-strength rubber band from your little brother, that type of thing.

COOLEY: Yeah, no, they like that sound, and that's - that sound of your saw is just about the right sound for whatever species you're pulling in, and they're coming to check it out.

FLATOW: All right, thanks for letting us know. So if you want to attract them, then take out some powered garden implements.

COOLEY: Yeah, get your weed whacker. You know, the ones that get attracted are the ones that have calling songs with pitches that are kind of up in the seven or 10 kilohertz range, kind of high and whistle-ly. And those weed whackers and all those sorts of machines make that kind of sound.

FLATOW: All right. Here's somebody who needs some advice. Holly(ph) in Brownfield, Maine. Hi, Holly.

HOLLY, CALLER: How are you?

FLATOW: Hi.

CALLER: Hi. Yeah. My daughter is scheduled to get married on June 8th in Maryland on the Chesapeake, outdoors in the evening.

COOLEY: Mm-hmm.

CALLER: Would you be looking for an indoor venue, or do you think we're good to go?

COOLEY: Well, there actually is a website that is the cicada wedding planner that...

CALLER: Aha.

COOLEY: ...for people with exactly your problem.

(LAUGHTER)

COOLEY: But, you know, it depends on where exactly you are, and one of the issues there, again, our maps are not very good for Brood II. If you're right down on the water, I would be surprised if you have a problem because the cicadas really don't like to be right down by the water.

CALLER: Good.

FLATOW: Good luck. Congratulations.

CALLER: (Unintelligible) some sprinklers.

(LAUGHTER)

COOLEY: Yes. Have a good wedding even...

FLATOW: Yeah.

COOLEY: ...if you don't get free music.

(LAUGHTER)

CALLER: Yes. Thank you very much.

FLATOW: Don't bring out the weed whacker at the wedding...

(LAUGHTER)

CALLER: No, no.

FLATOW: ...(unintelligible) cicadas, yeah.

CALLER: Thank you.

FLATOW: Happy wedding to you. If you - if they live on the roots of trees and shrubs, is it a bad year to plant them because they'll be out and going back underground?

COOLEY: Well, you know what I would say about that is you hear about these cicadas and all that. They really don't do a lot of damage to crops or anything like that. But the females do lay their eggs in twigs, and they really like twigs that are about pencil-sized. So if you're going to plant some young trees or if you have some fruit trees or something like that that are a little bit delicate and you don't want to be damaged and you do have the cicadas, you need to take some steps to prevent anything from happening to your trees.

FLATOW: Yeah.

COOLEY: And, you know, what we tell people is go to your hardware supply center or whatever and get this netting - they call it orchard netting or avian netting - and just wrap your trees up in that. Then the females can't get in there, and they can't lay their eggs, and there won't be any damage.

FLATOW: Very interesting. Let's go to Jen(ph) in Cincinnati. Hi, Jen.

JEN: Hi. I just have a comment about cicada season. I enjoy it because the firefly population seems to be spared by the predators when the cicadas are out, and it makes summer evenings so enjoyable.

FLATOW: They're busy eating the cicadas and not the fireflies.

JEN: Exactly. It just seems like...

COOLEY: That's an interesting point. Yeah.

JEN: ...they're in that 17-year cycle there. The firefly population is enormous as well. So I just assume...

FLATOW: You really notice the difference.

JEN: ...that it's because the birds are happy and glutinous on cicadas.

(LAUGHTER)

COOLEY: Well, that's a neat point. I hadn't thought of that before, but that makes sense.

FLATOW: There's a research paper for you.

(LAUGHTER)

FLATOW: Thank you. Jen, are they out there yet in - do we get to see them in Cincinnati, do you think, this brood?

JEN: They haven't come out yet but usually about mid-June.

FLATOW: Mid-June.

COOLEY: Yes. Cincy(ph) is out of range for the periodical cicadas this year, but Cincinnati happens to be sort of the epicenter of a whole bunch of other broods, like 10 and 14 and maybe even six down in that area. So you have to wait a few years to have periodicals down there. But Cincinnati is a good place. You can see a lot of different broods there.

FLATOW: Good luck, Jen.

JEN: Yes. Thank you. Thank you.

FLATOW: You're welcome. You're welcome. This is SCIENCE FRIDAY from NPR. I'm Ira Flatow talking with John Cooley, research scientist at the University of Connecticut in Storrs. Has anybody seen any yet?

COOLEY: Well, you know, we're doing the Citizen Science Initiative on the website, so we collect records that people send in. And we have some records that sound like it's starting down by Greensboro, North Carolina. People got photographs of adults and descriptions of adults. So I think it's on.

FLATOW: Wow. Has global warming affected their cycle at all?

COOLEY: Well, I think they're very sensitive to climate and certainly anything that lives in part of North America that was glaciated has responded to climate in the past. I would say that our current maps, again, are too coarse and too really inaccurate to allow us to make any kind of intelligent statement about whether they're going to respond to global warming. Obviously, if the climate changes, they will respond, but we don't have any signal that shows up yet in the records, mostly because the records aren't that good.

FLATOW: Are both the male and the female making the same noise, or is it just one?

COOLEY: No. Actually, when you hear that sound out there, you're hearing about half the population because only the males make that sound. The females signal, but they make other kinds of sounds. They don't have the organs to make that loud sound, so the females signal by flicking their wings.

FLATOW: And can you tell different species just by looking at them?

COOLEY: You can. There are some morphological differences, especially in the coloration of the underside of the abdomen, but you can really tell the species apart by the sounds.

FLATOW: You can.

COOLEY: They have different sounds.

FLATOW: You can. Can - will people mistake them for crickets maybe at night, they come out?

COOLEY: I would guess probably not. They're going to be out earlier than many of the crickets that we have in North America, and they're also day singers. And a lot of our crickets are night singers. So if you hear a loud thing singing during the day, it's more likely to be a cicada than a cricket.

FLATOW: Interesting. Let's go to Chino(ph) in Fredericksburg, Virginia. Hi, Chino.

CHINO: Hi. This is Chino. I'm calling from (unintelligible), Washington. I wanted to know - we know how earthworms contribute to soil health, and you were saying that they spend 17 years, you know, eating stuff. Is it understood the value of cicadas to the soil health is an indicator? Is the lack of cicadas an indicator of bad health or something like that?

COOLEY: Yeah. There's a couple of points that you can make about that. I would say that the cicadas are an indicator of something along the lines of forest health because they require reasonable patches of deciduous forest. But your point about soil is also excellent because these cicadas are physically transporting things like nitrogen and phosphorus from below ground to above ground. So they're taking some of the essential nutrients that everything out there needs and moving them around and making them available to other species in other places.

FLATOW: Mm-hmm. How about also aerating? They're sort of come out of the soil?

COOLEY: Yeah, they do. Yeah. It looks like Swiss cheese when they're done with it.

FLATOW: Is that right?

COOLEY: Oh, yeah. If you really have them, you're going to have a Swiss cheese kind of situation under certain trees.

FLATOW: All right. So for all of us waiting, give us some tips on how to look for them. You won't certainly have any problem hearing them, right?

COOLEY: No, you wouldn't have any problem hearing them, but the signs will start well before then, and the first thing that shows up is the holes. They'll make those holes well before they come out, and you'll start to see these open up, and they're about the size of, say, your little finger. It's very tempting to want to go stick your finger down in these holes. And if nothing bad happens, it's probably a periodical cicada hole because the cicada will just sit down there and wait. And then one evening, within the next month or so, that cicada down in that hole is going to come out, and you'll start to see the shells that those cicadas will shed, and then you'll start to hear the chorus. And roughly a month after you start really hearing the chorus, then it's all going to end.

FLATOW: Well, so it's a little bit something to look forward to.

COOLEY: Absolutely.

FLATOW: All right. Thank you, John, for taking time to be with us today.

COOLEY: Thank you very much.

FLATOW: Dr. John Cooley, research scientist at the University of Connecticut in Storrs. We're going to take a break. And when we come back, we're going to talk about, oh, antimatter. It's going to be really interesting. Does it go down when you drop it, or does the anti go up? Experiment, we'll talk about it after this break. Stay with us. I'm Ira Flatow. This is SCIENCE FRIDAY from NPR.

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