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This week in science: Invasive ants, ancient chewing gum, and return of the cicadas

JUANA SUMMERS, HOST:

It's time now for our regular science news roundup with our friends at NPR's Short Wave podcast, Regina Barber and Pien Huang. Hey, y'all.

PIEN HUANG, BYLINE: Hey, Juana.

REGINA BARBER, BYLINE: Hey.

SUMMERS: So how this works is you've brought us three science stories that caught your attention this week. Tell us what they are.

HUANG: Yeah. So first off, we've got a story about how a bunch of tiny, invasive ants have changed how elephants act and what lions eat.

BARBER: Then we have a sample of ancient chewing gum that tells us about dental care and diets in the Stone Age.

HUANG: And then, billions of cicadas are appearing this spring.

SUMMERS: OK. There is a lot going on here. I kind of don't want to pick between them, but OK, let's start with ants and lions.

HUANG: OK. So this story starts on the savanna at a nature preserve in central Kenya. And, Juana, if we went back 20 years, we would see grasslands that are covered with acacia trees.

BARBER: And these trees provide food and shelter for native ants. And in turn, the ants defended the trees against animals that would eat the trees, like elephants. Like, when elephants would grab tree leaves, the native ants would swarm up inside their trunks and bite them.

SUMMERS: This does not sound fun.

BARBER: No, no, not at all. And for a long time, the trees and the ants had this, like, mutualistic relationship.

HUANG: And then about, like, 20 years ago, this new, invasive ant showed up. It's called a big-headed ant. And it starts taking over the territory, killing the native ants and leaving these trees undefended.

SUMMERS: OK. I think I know how the story goes. Let me guess here. The elephants are running rampant on these trees.

BARBER: Yeah. They are. They're not just eating the leaves. The elephants are pulling down the branches. They're knocking the trees over. And Douglas Kamaru - he's an ecologist at the University of Wyoming. And he says that these elephants have torn down so many acacia trees that they've transformed the landscape.

DOUGLAS KAMARU: Now we are seeing, like, these areas opening up from the dense we're talking about in terms of those acacias to more open landscape, like a grassland or something like that.

BARBER: And he says elephants have cleared 70- to 80% of the trees in the park. And this is all over the last 20 years.

SUMMERS: OK. We mentioned that the story is also about lions, so help us fit that part of the animal kingdom in here.

HUANG: Yeah. Right. So for the lions at this park, their favorite food is zebra. And the lions usually catch the zebras by hiding behind trees, stalking them, and then, boom, they pounce. And this open landscape - it means that they're losing the element of surprise. I mean, the zebras can now see them coming from across the field, and they get plenty of time to escape. So Kamaru and his team actually found that the lions were almost three times better at hunting zebra in that tree-covered area, like what the whole park used to be, than on the open grassland that's there now.

BARBER: And this took years of fieldwork and observations and experiments to figure all this out. It's all detailed in the journal Science this week. And one outside researcher who wasn't involved in the work told us that these connections in ecology can be really messy. But she was impressed with how well the study documented these links.

SUMMERS: Got a question for you. What does this all mean for the lions? I mean, if they can't catch the zebras, are they starving?

HUANG: Well, it turns out that there's actually some evidence that they're switching their diets. So as the proportion of zebra in their diet goes down, the amount of buffalo has gone up. So that means that, so far, the lion population seems OK. Like, their numbers are stable. There are still places in the park with tree cover where they're having decent luck catching zebras, but these tiny, invasive ants are still taking over the park at a rate of about 160 feet a year, and it's not clear if they can be stopped.

SUMMERS: All right. Next up, I think you all have brought a story about something that does not sound particularly tasty to me - Stone Age chewing gum.

BARBER: Yes. That's right. But, Juana and Pien, I'm really curious. What's your opinion on gum? Like, do you love it? Do you hate it?

HUANG: I'm going to go with love it. I love Bubble Tape.

SUMMERS: I absolutely cannot stand it.

BARBER: Oh, no. I love gum. I have, like, packs all over my house, in my car. But most relevant to this study, my teenager loves it, too.

SUMMERS: OK. I live with teenagers, too. That sounds like something that could get very messy in a kid's room. But please explain. What do teenage gum preferences have to do with the Stone Age?

BARBER: So it's because the study, published in the journal Scientific Reports, looks at what teenagers ate in Scandinavia about 10,000 years ago. And this is all by analyzing the ancient gum they chewed.

SUMMERS: OK. What flavor of gum are we talking about here 10,000 years ago?

HUANG: Well, I mean, gum was a different thing back then. You know, basically it was tar made from the bark of birch trees. And people in the Stone Age used to chew a wad of this and then maybe, like, stick some tools together with it. And as you chew gum, in general, it collects stuff from your mouth - you know, genetic material, bacteria, little bits of food stuck in your teeth. And so this Stone Age wad of gum is something like a time capsule of what they were eating.

SUMMERS: OK. I am going to need to hear about the menu in Stone Age Scandinavia.

BARBER: Yeah. I was very interested. So I asked an archeogeneticist at Sweden's Stockholm University about this, Anders Gotherstrom. Here's what he said people were snacking on in the middle Stone Age, or Mesolithic period.

ANDERS GOTHERSTROM: So what's a proper Stone Age diet? At least now we know that if you go home and put hazelnuts, trout and deer in your frying pan, then you would have a Mesolithic diet from Scandinavia.

HUANG: And this gum also has, like, the imprints of teeth, which gives you the size of the teeth, which is also how they knew that the gum-chewers were teenagers. And Gotherstrom and his team could tell from the mix of bacteria in the gum that one of the teens actually had very bad gum disease.

GOTHERSTROM: We know that she was about to lose her teeth.

SUMMERS: Ouch, although I guess it's not super-surprising that someone who lived almost 10,000 years ago needed some dental work.

BARBER: Yeah. Gotherstrom said that she probably was in a lot of pain while chewing that gum. And while that's very sad for her, there's this little silver lining for researchers in the fact that we can learn so much detail of the daily life of a Stone Age person from a small piece of gum.

SUMMERS: Interesting. All right, let's move on now to cicadas. And I should just point out that this topic is such a big deal in my household. My husband absolutely loves cicadas. But I'm going to let you guys explain.

BARBER: Yeah. So scientists have determined that this spring, two adjacent groups of cicadas will emerge at the same time all across the Midwest and the Atlantic states, meaning billions of cicadas at least. Our colleague Clare Marie Schneider wrote about this, and one entomologist she talked to described it as a spectacular, macabre Mardi Gras.

SUMMERS: OK. So this sounds like my kind of party, but I should note that not everyone would probably love this. So tell us. Are these the kind of cicadas that come up every summer, or is this something more special?

HUANG: OK. This is more special. I mean, there are annual cicadas, but these are more rare. So these two regional groups, or broods, of cicadas only emerge every 13 or 17 years. And the really exciting thing here is that the last time that these two specific broods - again, one on a 13-year cycle, the other on a 17-year cycle - the last time that they came up at the same time was in 1803.

SUMMERS: That is a long time ago. OK. Can one of y'all remind me how their life cycle works? - because 13 or 17 years - that is a long time to stay underground.

HUANG: It's a super-long time. Yeah. So periodical cicadas spend all of that time underground in this immature nymph form where they're sucking on the roots of shrubs and trees and feeding. And when that time comes, they emerge. They molt. The males have this, like, glorious cacophony of calls and songs, which can actually be louder than a jet engine. And then these cicadas mate. The females lay their eggs in trees.

BARBER: And the cycle starts all over again, like, when the eggs drop from the tree and return to the ground for another 13 or 17 years.

SUMMERS: So tell me. When exactly does this cicada Mardi Gras kick off?

BARBER: So one brood will start appearing in late April, mostly in the South, and the other will appear in mid-May around Illinois, Wisconsin, Indiana and Michigan.

SUMMERS: All right, guys. I am setting myself a reminder to book a plane ticket back to the Midwest for that.

(LAUGHTER)

BARBER: Awesome.

SUMMERS: That is Regina Barber and Pien Huang from NPR's science podcast Short Wave, where you can learn about new discoveries, everyday mysteries and the science behind the headlines. Thanks to both of you.

BARBER: Thank you, Juana.

HUANG: Thank you.

(SOUNDBITE OF RUN THE JEWELS SONG, "GET IT") Transcript provided by NPR, Copyright NPR.

NPR transcripts are created on a rush deadline by an NPR contractor. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of NPR’s programming is the audio record.

Regina G. Barber
Regina G. Barber is Short Wave's Scientist in Residence. She contributes original reporting on STEM and guest hosts the show.
Pien Huang
Pien Huang is a health reporter on the Science desk. She was NPR's first Reflect America Fellow, working with shows, desks and podcasts to bring more diverse voices to air and online.