09/15/2017

When Dung Is What’s For Dinner

17:42 minutes

Credit: Jordan Kirtley

Dung and carrion beetles dine on dead animals and defecation of all kinds. That might seem like unappetizing fare to us, but the dining preferences of this cleanup crew are an essential part of how nutrients cycle through the natural world. In this interview recorded live at the Orpheum Theater in Wichita, Kansas, graduate researchers Rachel Stone and Emmy Engasser take us on a tour of the beetles inhabiting the Kansas prairie, and explain why everyone should have an appreciation for these bugs.

SciFri journeyed out into the field with Stone and Engasser to hunt for dung beetles.


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Segment Guests

Rachel Stone

Rachel Stone is a graduate researcher in the Biodiversity Lab at Wichita State University in Wichita, Kansas.

Emmy Engasser

Emmy Engasser is a graduate researcher in the Biodiversity Lab at Wichita State University in Wichita, Kansas.

Segment Transcript

IRA FLATOW: This is Science Friday. I’m Ira Flatow, coming to you from the Orpheum Theater in Wichita, Kansas.

[APPLAUSE]

Yes.

And as a reward for all of you who have stayed and watched the program, we now have a special for you. We’re going to talk about recycling, as you know, is very much a part of daily life these days. You got your bins for paper, for glass, for plastic.

But we humans weren’t the first. No we didn’t come up first, the first ones with the idea. Nature has had its own recycling system for eons. And hey, maybe you never pondered this. I know I didn’t before I got to Kansas. Where do you think the cow patties go after they come out of a cow? We city slickers didn’t think about that very much. Do you think they just sit there and disintegrate in the sun?

Well it turns out that nature has a sophisticated cleanup crew. Insect workers, like dung beetles, and Carrion beetles that make dead animals and dung and all sorts of decaying stuff disappear, and return back to the soil so other living things can use them. So after you hear about the dirty work they do you might have a little more appreciation for these tiny recyclers. I know my next guests do. You might even say they have beetle mania.

[GROANS]

[APPLAUSE]

I deserved that one. Rachel Stone is a graduate researcher in the biodiversity lab at Wichita State University. And [APPLAUSE] so is Emmy Engasser. She’s also a graduate researcher at the biodiversity lab at Wichita State. Welcome both to Science Friday. [APPLAUSE] Rachel, let’s start off with the object of your heart’s desire–

RACHEL STONE: Yes.

IRA FLATOW: Dung beetles. Oh yes, clasping your heart. What do you find so special about them?

RACHEL STONE: Dung beetles have captivated humans for as long as we’ve been around. You can think about early Egyptians, and how they revered this god, the Kheper god, that carried the sun across the sky. You see the scarab beetle represented in films all the time, like it’s unfair villainization in The Mummy movie, if you guys recall that.

It was also the beetle that got Charles Darwin to start to ponder that idea of sexual selection, for example. These are really, really important, cool beetles. So I, like many others, fell in love with them.

IRA FLATOW: They actually perform a great service.

RACHEL STONE: They sure do. They’re unsung heroes of all ecosystems, they really are.

IRA FLATOW: Well, we’re singing about them today. And I think less people think insects are of a lesser intelligence. Is it true, isn’t it that dung beetles can even navigate by the Milky Way?

RACHEL STONE: They sure do. There have been studies where scientists put, if you can imagine, adorable little hats that covered their eyes, they could no longer navigate. They would wander in circles. But whenever those are removed, they can go in a straight path, using the sun and using the Milky Way at night.

IRA FLATOW: Wow. Not to be outdone, Emmy, I understand that you’re more interested in what shows up for dinner when an animal dies.

EMMY ENGASSER: Exactly, yes.

IRA FLATOW: The Carrion crew. Tell us about your interest in this.

EMMY ENGASSER: The Carrion beetles are also very interesting because they eat really disgusting stuff. And they show up to these dead carcasses really early, even like seconds or hours after these animals die. And they are there to feed and make babies. And so it’s very interesting because if we didn’t have them we would have a lot of dead animals just littering the earth. So they’re very important in decomposing.

IRA FLATOW: I hate it when that happens.

EMMY ENGASSER: Yeah, same with dung, too. We don’t want to be stepping in that stuff.

IRA FLATOW: Is there a progression of the insects when an animal dies.

EMMY ENGASSER: Yes, definitely. Flies probably are the first ones to get there, but the Carrion beetles want to get there first, too. And there’s this whole slew of insects that are there at all different times during the decomposing stages.

IRA FLATOW: And in case you’re all wondering about how excited people can get about dung beetles, let me take you along on a bug hunting field trip with Emmy, Rachel, and one of our graduate advisors Mary Liz Jameson, one of your graduate advisors.

MARY LIZ JAMESON: So the creek is over here. And then there’s these buckets, which we have baited with various yummy selections. This is Lou poo.

EMMY ENGASSER: Lou poo!

MARY LIZ JAMESON: Canine poo. And then, after that is gizzards for Emmy’s stuff, and then the far one is human carnivore poo. So carnivores and herbivores bring in, in most situations, different kinds of dung beetles.

EMMY ENGASSER: What’d my girl bring in?

RACHEL STONE: Let’s look at it!

MARY LIZ JAMESON: OK!

EMMY ENGASSER: I want to see.

EMMY ENGASSER AND RACHEL STONE: Ooh.

RACHEL STONE: Cool.

MARY LIZ JAMESON: Do you want me to go get the forceps?

RACHEL STONE: It’s OK, I’ll get my finger [INAUDIBLE].

MARY LIZ JAMESON: Ooh, that’s not who I thought it was.

EMMY ENGASSER: Yeah, it’s geotrupes.

MARY LIZ JAMESON: Yeah.

RACHEL STONE: It’s an eleodes.

MARY LIZ JAMESON: Oh, stink beetles. They’ll put their butt in the air and stink on you, so you won’t eat them.

RACHEL STONE: Kind of fruity, and unusual.

MARY LIZ JAMESON: But they are really neat when you start to look at stuff. I mean, I think it’s one of the reasons why prairies are conserved, because people don’t sit on the ground and look closely at stuff. But when you do, all of a sudden, there’s whole worlds that open up in front of you.

IRA FLATOW: Wow, that was one heck of a field trip.

[APPLAUSE]

IRA FLATOW: I detected the phrase human carnivore poo. Is that what I think it is?

RACHEL STONE: Yeah we have to separate the human carnivore from the human herbivore, the vegetarians of the world. We’re all bait producers for beetles.

[LAUGHTER]

IRA FLATOW: So these are equal opportunity beetles.

RACHEL STONE: Absolutely.

IRA FLATOW: Some like carnivore poo, some like vegan poo?

RACHEL STONE: You know, we’ve never tried that in the lab, but we should look into it.

IRA FLATOW: Now I understand that on your way back from the field the other day, you came across an interesting specimen on the side of the road.

RACHEL STONE: We sure did.

IRA FLATOW: And instead of driving by and averting your eyes, like most people would do, you stop the car and you went to investigate. What were you looking for?

RACHEL STONE: We were looking for silphidaes, the Carrion beetles. And we were met with many writhing maggots instead. But, we believe that this carcass was a little bit too far gone for the Carrion beetles to be there. It had been mostly eaten by the maggots. It was amazing to see they were just

EMMY ENGASSER: Everywhere.

RACHEL STONE: They were so thick under the deer that you could hold your hand up and feel heat coming off of this writhing mass. It was cool.

EMMY ENGASSER: It was really cool.

[APPLAUSE]

IRA FLATOW: I guess it’s cool depending on whether you’ve had dinner yet or not.

[LAUGHTER]

You know, I’ve seen some dung beetles with little spikes on their heads. Why is that? Is it just decoration or something?

RACHEL STONE: That’s a beautiful example of one right there. This is a male phanaeus vindex. They’re gorgeous beetles. But you’ll see these incredible horns structures that will actually vary within a single species on all the males. So you’ll have tiny little nubs of a horn, just little suggestions, and then huge long horns like you see here.

IRA FLATOW: It almost looks like a rhinoceros.

RACHEL STONE: Yeah, absolutely. But those horns serve a purpose for this specific group. These guys exhibit a behavior where they tunnel under a dung pat. And you’ll see different kind of behaviors with different kind of dung beetles. So the famous ball rolling that dung beetles do, that’s a separate group. But these guys will tunnel down, and those horns serve as this big obstacle. And they protect their tunnel, and they’ll block others from passing through to get to the dung resource.

IRA FLATOW: How deep do they tunnel?

RACHEL STONE: It depends on the species. Some can go quite deep. There’s huge dung beetles in Africa that can dig tunnels. Some are documented as deep as eight feet underground, and others you can just dig out with your finger and get them out, a couple of inches.

IRA FLATOW: Well, Emmy, let’s talk about continue our battle of the beetles here. How fast can Carrion beetles scout out a corpse, and how do they know it’s there?

EMMY ENGASSER: As you know insects have antennae, and these Carrion beetles have these clubbed antennae. And what they can pick up, chemical senses in the air, odors, and so they use those chemo receptors on those clubbed antennae to find the carrion. And some of them choose to bury those carcasses like the burying beetles. And then some of them, also, will just hang out on the carcasses, eat a little bit here and there, and then they’ll lay eggs underneath the carcass. And their babies will just stay there and eat on those carcasses.

IRA FLATOW: Wow. I just touched on this briefly, Rachel, but I want to get my hands a little dirtier, so to speak. I mean, there are a lot of different kinds of animals, different things that are dying, different things that are pooping. Are their specialized beetles for all these different things?

RACHEL STONE: There absolutely are. There’s dung beetles that have a really broad palate. They’ll eat any kind of dung they can find.

IRA FLATOW: That’s an interesting way of phrasing it. [LAUGHTER]

RACHEL STONE: There’s others that are more persnickety. For example, there are dung beetles that eat only the dung from sloths.

IRA FLATOW: Really?

RACHEL STONE: Yeah.

IRA FLATOW: That’s specialized

RACHEL STONE: It’s very specialized

IRA FLATOW: Wow. Let’s see, I’m sure we have a question or two in the audience about this. Let me go right here.

AUDIENCE: Hi I’m wondering if there’s a special quality that these bugs have that enables them to not get sick when they eat this stuff. And if so, could we take that, and give it to my kids when they don’t wash after they go to the bathroom?

[LAUGHTER]

[APPLAUSE]

EMMY ENGASSER: Yes, so Carrion beetles do definitely have bacteria in their gut flora. And so I would imagine that they are completely adapted to eating these dead animals, and they don’t get sick from eating them. It would be really interesting to look at applications for helping upset stomachs, but as far as I know, there haven’t been any cures for upset stomachs from Carrion beetles.

IRA FLATOW: As a show, we always talk about the microbiome a lot, so we’re really sensitive to bacteria a lot. And I noticed, in this field trip that you took, no one was wearing any gloves going in. So you just go right in, so there must be E. coli all over those beetles, right? And you’re going right in there.

RACHEL STONE: Yep, absolutely.

IRA FLATOW: No fear.

EMMY ENGASSER: We’ll get our hands dirty.

IRA FLATOW: You wash your hands at least when you get home.

RACHEL STONE: We’ve got Purell in the car.

[LAUGHTER]

IRA FLATOW: So let’s talk about the beetles themselves. Do they make their own dung, and do other beetles go after their dung?

RACHEL STONE: I don’t know of any beetles that go after dung beetle dung. That would be fascinating. But as of now, I know of none. Those get decomposed by fungi and microbes in the environment. So those are the guys breaking down, not that kind of poo.

IRA FLATOW: That’s great. This is Science Friday from PRI, Public Radio International.

[APPLAUSE]

IRA FLATOW: Let’s go to a question here. Yes, someone at the mic?

AUDIENCE: How far away from a carcass can they still detect it?

EMMY ENGASSER: Carrion beetles can detect up to one to two miles away. They can smell the rotting carcasses, so it’s actually really far.

IRA FLATOW: So if they’re upwind, that goes with the wind then.

EMMY ENGASSER: Yeah, and they’re flying right to it. I know the American burying beetle can fly almost to one kilometer in a night. So they’re actively searching for that carrion, those dead animals to eat.

IRA FLATOW: Do they signal each other, hey, there’s a meal. You know like bees talk to one another?

EMMY ENGASSER: I don’t think so, because that would be more competition, because they have to fight over that resource. Because it’s a very limited resource to find those dead animals, those decaying tissues. So they don’t want to attract other beetles except for maybe a female. But they don’t want other males showing up.

IRA FLATOW: Let’s go to a question right here.

AUDIENCE: I’ve seen many pictures of beetles rolling their dung. Why do they roll it that way?

RACHEL STONE: Well what they’re doing is they’re going to this pile of poop, is suddenly plopped on the ground. And you have to imagine it like it’s this incredible resource, that’s like you’re in the desert there’s no food at all. And somebody drops this tray of cheeseburgers on the ground.

[LAUGHTER]

And everybody is rushing all at once, and they’re greedy. They want their fair share of this really limited resource. And so this is just one strategy that dung beetles show. But what he’s doing is, he’s trying to tear a hunk off for himself, and take it away from all the chaos of that pile of cheeseburgers, or poo. And he’s taking it away so he can have it himself.

IRA FLATOW: When we spray our crops with insecticides are we killing the dung beetles?

RACHEL STONE: We are. Also, when we’re treating livestock with things like Ivermectin that kills intestinal parasites, which is a good thing, it also has effects on the insect community within the environment. So primarily dung beetles are hurt by that. And then you have the problem of these cows that are feeding, and they’re pooping everywhere, and then there’s no dung beetles there anymore to eat that poo and deal with it. And then you have flies come in, and flies, of course, cause vector human disease. So it’s a whole other issue to worry about. It causes a lot of problems.

IRA FLATOW: Wow, you don’t think about that. Let me see if I can get one or two more questions. Yes, right here.

AUDIENCE: I’m asking this for my brother. So this is a question for both of you. Why are the beetles so brightly colored?

RACHEL STONE: That’s a great question.

EMMY ENGASSER: For the Carrion beetles they, a lot of times, have these orange or yellow patches on them, and that’s warning coloration. Because what they want to do is deter predators from eating them, because they stink like rotting flesh. And so they’re trying to get those predators to not eat them.

IRA FLATOW: Now you mentioned that one beetle in this field trip we heard that it turns its back side up, and what happens?

EMMY ENGASSER: It’ll musk you.

RACHEL STONE: Yeah.

EMMY ENGASSER: It lets out a foul stench so that you don’t want to mess with it.

RACHEL STONE: It’s not so bad.

EMMY ENGASSER: Well, yeah. Not to us. We’re used to it by now.

IRA FLATOW: I can’t think of a better way to end this segment. Can’t top that comment. Thank you both. Rachel Stone and Emmy Engasser, both graduate researchers at the biodiversity lab at Wichita State University. Thanks again for highlighting your work for us tonight. Everybody liked it. [APPLAUSE]

After the break, we’ll talk about how scientists use DNA and stone tool artifacts to piece together the story of the first Americans. And playing us to the break, Shane Marler and Nicky [INAUDIBLE].

[MUSIC PLAYING]

IRA FLATOW: This is Science Friday from PRI.

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