Every Thirteen Years, Brood Nineteen Is Back

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IRA FLATOW, host:

You're listening to SCIENCE FRIDAY. I'm Ira Flatow.

This time, up next, something a little more swarmy. This is the time of the great reemergence, and I'm not - nothing to do with the end of the world. I'm talking about cicadas. From the American South up to Maryland and as far west as Iowa, periodical cicadas are making their once every 13-year appearance. In some places, they're already here, and, of course, you would know that if you are in those places. In others, their presence is still yet to be felt over the next couple of weeks.

And joining me now is John Cooley. He's a researcher at the University of Connecticut at Storrs. He runs the magicicada.org website where he's tracking reports of the emergence, and he's on the road looking for cicadas. He joins us from Dixon Springs Agricultural Research Station in Illinois.

Welcome to SCIENCE FRIDAY.

Dr. JOHN COOLEY (University of Connecticut, Storrs): Thanks. It's a great pleasure to be here.

FLATOW: Now, you're actually out on the road looking for them?

Dr. COOLEY: Yeah. I'm actually, though, to be honest, taking a day or two off from being on the road. Since the project started, I've driven over 9,000 miles, and I'm getting a little road weary.

FLATOW: How do you look for them?

Dr. COOLEY: Well, you don't really have to look too hard. You listen. Because when they're out, they make a lot of noise.

FLATOW: And why are these different cicadas than the kinds we hear every summer?

Dr. COOLEY: Well, these are periodical cicadas, and that means a couple of things. It means they come out in massive numbers, so you're talking about millions per acre. That's the figure in the literature. They also only come out as adults once every 13 or 17 years. And in the intervening years, they're just not there. And they had, you know, they have synchronized development. They have very characteristic appearance. They're really just not like the other cicadas.

FLATOW: And these are called the Brood XIX emergence, correct?

Dr. COOLEY: Yes. That's correct.

FLATOW: Where did you get Brood XIX from?

Dr. COOLEY: Well, you know, there was a lot of work in the 19th century trying to understand these cicadas a little bit better, and there have been records of the emergences going back to the 1600s.

There was a real attempt by the entomologist Charles Riley to start organizing these records. That was later picked up by Marlatt, working for the USDA later on, and they came up with a scheme for organizing the emergence records, and they decided to use Roman numerals.

And they just picked an arbitrary starting point. That's Roman numeral I. That's the brood that's coming out next year in the Blue Ridge, and they counted up to XVII from there. Those are all the 17-year cicadas. And XVIII through XXX are the 13-year cicadas.

Now, it turns out there are only three broods of 13-year cicadas, and that's XIX, XXII and XXIII.. But all those other slots were kind of opened on the basis that there might be broods there.

FLATOW: Yeah. Now, why is this one called the granddaddy of them all?

Dr. COOLEY: Well, I think because it really covers the largest geographic extent, and it's just not an exaggeration to say these are out from Maryland down into Georgia over - practically over to Texas and up to Iowa. It's just an enormous area.

FLATOW: And so when do they emerge, and what causes - what's their timing all about?

Dr. COOLEY: Well, you know, the research that's been done, and you can appreciate this is a little bit difficult to study, suggests that they're able to count the annual cycles of their host plants. So they're living underground, feeding on plant roots and they have some way of counting those cycles. We don't really know how.

Then, they get to the right year that way, and in the right year, they're monitoring soil temperature. And the figure that you see in the literature is they're waiting for the temperature to get to be about 62 degrees Fahrenheit, and then, the nymphs come out of the ground and molt to be adults, and the emergence is on.

FLATOW: And you're out there in Illinois where they're emerging.

Dr. COOLEY: Yeah. You know, we're really not at the peak yet because the weather has been a little bit off.

(Soundbite of laughter)

Dr. COOLEY: I have to say it's been kind of cool and rainy.

FLATOW: It has been whacky whether.

Dr. COOLEY: All you out here, you know what I'm talking about.

FLATOW: Yeah. Yeah. And so will they be emerging in the South then where it's a little warmer?

Dr. COOLEY: Oh, yes. They're full blown out in some places in the South. We were in Nashville a couple of days ago, and there's some good choruses going there. Certainly down in Montgomery, Alabama; Meridian, Mississippi, all those places have good choruses going in. We have the nymphs just starting to get going up here in Illinois.

FLATOW: And how long do they live for so that we can know when the symphony is over?

(Soundbite of laughter)

Dr. COOLEY: Well, of course, you know, the simple answer to that is 13 years, but as adults, they last on the order of, I'd have to say four-ish weeks, a month is a good rule of thumb.

FLATOW: Why would an animal choose to sit out for 13 or 17 years? What is the advantage of staying away so long?

Dr. COOLEY: Well, you know, that really is kind of the key question, and I have to be honest with you, we don't have any simple answers to it. We suspect that, if we do ever find out the answer to that, it's going to be related to the unusual biology of these cicadas. They rely on massive numbers to avoid being eaten

They rely on massive numbers to avoid being eaten by predators. It's kind of like an insurance policy. We call it predator satiation, but what it really means is the individual risk to a cicada is zero because there are so many of them. The predators can go there and eat all they want and the risk is still zero to the individual cicada. So they're coming out periodically to accomplish that, these mass emergences.

The long life cycle, that's a little bit harder to figure out. To be honest, we don't know the life cycles of many cicadas, perhaps they're all long. The interesting thing about 13 and 17 is their primes. And I have some colleagues working on some papers, some mathematical models to figure out whether this prime numbered life cycles really lend themselves to having these mass periodical emergences with no adults out in between.

FLATOW: Mm-hmm. Well...

Dr. COOLEY: That's the key to the thing.

FLATOW: ...that's interesting. And you are sort of crowd sourcing the sightings, are you not? You're looking for people if they see that emergence, to let you know.

Dr. COOLEY: Yeah. We're definitely encouraging people to report sightings on the website because, to be honest, we're working on maps that are very old. They're from the 19th century.

FLATOW: They're made out of paper.

(Soundbite of laughter)

Dr. COOLEY: Well, yes. They're not at all electrons.

FLATOW: Right.

Dr. COOLEY: We'd like to update those. A lot of the questions about periodical cicadas have to do with whether the edges of broods or species are moving. And we can't tell that from the old maps.

FLATOW: And so, if we go - you go to our website at sciencefriday.com, they'll have a link to your website and people can report in when they hear the emergence. Will they know the difference between their ordinary cicadas and these when they hear them?

Dr. COOLEY: Yeah. There are pictures on the website. It's kind of radio-button thing where you see a picture and you click under it. And you'll know it because of the numbers. For those of you who haven't been through one of these emergences, I guess you're in for a treat. But you certainly are in for something unlike anything you've seen before.

FLATOW: Let's go to Steve in - back in Cherry Hill, New Jersey. Hi, Steve.

STEVE (Caller): Hi. My question was simply, how old do they possibly make that much noise? I mean, I know it's the numbers in this particular case, but I've heard individuals, you know, like outside in my tree, and it's quite a noise...

FLATOW: Well, yeah. Yeah.

STEVE: Just the explanation.

FLATOW: What - got a good question. Thanks for calling. What is that explanation?

Dr. COOLEY: Well, the - only the males are making the noise, so you're only hearing half the population.

FLATOW: Isn't that true of everything?

(Soundbite of laughter)

Dr. COOLEY: Yeah. It's just about, I think. They have a pair of special organs on the first abdominal segment called tymbals. It looks like a little potato chip. If you pick one up and bend the wing back, you're going to see it there. It's a little white membrane. And that's the noisemaker. And the abdomen is a hollow resonator and a sound radiates out through to openings on the bottom.

The funny thing is, these cicadas, individually, really aren't that loud. It's the aggregate numbers that get the sound up in these choruses.

FLATOW: Mm-hmm. Let's go Sharon in Philly. Hi, Sharon.

SHARON (Caller): Hi. I actually have a statement first. When I was a kid, that song by Glen Campbell, the "Wichita Lineman," you know, the sound comes through the Wichita Lineman is still on the line. It's something about the sound coming through the wires. And I was very young, OK? But I would hear cicadas and I thought, oh, that must be the sound from the lineman coming, you know, through the wires. And I said, Oh, my goodness when I really found out what the sound came from.

But anyway, the reason I was calling is, killer wasps, we found them a couple of years ago after moving to an old farmhouse. And I found out that they were called killer wasps, but I didn't know, you know, who they attacked or why they were told to. But apparently, they attack cicadas or eat them. Are they like a primary source of a...

Dr. COOLEY: Food source.

SHARON: ...you know, is the cicada their primary source or is that, you know, a primary predator for the cicada?

Dr. COOLEY: Sure. Cicada killer wasps are, again, fascinating insects. They do specialize on cicadas. They will take periodical cicadas. They're also very good predators of our summer cicadas, our dog-day cicadas. And the wasps, the female wasp, will capture a cicada, drag it down into her burrow and just about like something in a horror movie, lay her eggs on it. The eggs hatch and the cicada sitting there paralyzed but still alive and the larvae eat their way through it. It really is the stuff of horror movies. That said, you know, with the periodical cicadas, there just aren't enough wasps to really make a dense in the population.

FLATOW: Mm-hmm. Just to reiterate, though, these are not these flying locust that people confuse, what, every 17 years or something like that.

Dr. COOLEY: Yeah. You know, that's funny too. These are not locusts. Locusts are grasshoppers, but the name got stuck on to them because the puritan colonists in Massachusetts in the 1600s witnessed the periodical cicada emergence and pretty much thought the end of the world was coming.

FLATOW: Wow. So, we here in New York, we have yet to hear them or they're out -they're not out yet?

Dr. COOLEY: Well, in New York State, certainly the areas around New York City, you're in Brood II territory, that's 17-year cicadas. And you'll be seeing them in about 2012.

FLATOW: Oh, something to look forward to. And where will your travels take you next?

Dr. COOLEY: Next? Well, I need to get down to Arkansas and have a look there. And 13 years ago, my colleagues and I discovered a new species down there, and we're going to see what it's been up to. It actually happens, also, to be at the spot in Dixon Springs. I caught a few of them this morning.

FLATOW: And what would you like to know most about them? It does - you seemed to say that we really don't know that much about the cicadas.

Dr. COOLEY: Well, you know, I think anything that we do in science we always raise more questions than we answer. But I - you know, if I had a time-lapse movie of what these cicadas did during the past couple of glacial cycles, that would make me happy because I - the species are old but the territory they live in is not. It was all glaciated. They're affected by glaciers. I'd like to know where they spent the last, I don't know, 25, 30,000 years.

FLATOW: Is there anyway to find that out?

Dr. COOLEY: Well, there are various ways to get at that peripherally by looking at the genetic structure of the populations and by looking at the distributions. Or also doing some ecological modeling of the distributions. But, you know, time lapse movie would make it simple.

FLATOW: Wow. That would be cool. Can you see a time lapse movie of a cicada emerging, anyway?

Dr. COOLEY: Well, yes. Actually, people would like to shoot that. I know that there was a sequence of that in a BBC series a couple of years ago. And someone is coming out, Monday, to shoot a time lapse of a cicada coming out of the ground.

FLATOW: All right. Well, sounds like you have an exciting week ahead of you.

Dr. COOLEY: And a lot of people have an exciting month ahead (unintelligible)...

(Soundbite of laughter)

FLATOW: Well, we're looking forward to it. Thank you for taking time to be with us, and happy cicada hunting.

Dr. COOLEY: Oh, no problem at all.

FLATOW: May you be very successful.

Dr. COOLEY: Well, thank you very much.

FLATOW: John Cooley is a researcher at the University of Connecticut at Storrs. And he's finding out more about insects. And you can report - if you see this -you can report the cicadas to magicicada.org. Our website, also, has a link.

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Source: http://www.npr.org/2011/05/20/136501160/every-thirteen-years-brood-nineteen-is-back?ft=1&f=1007

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