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This week on the SciShow Talk Show Doug Emlen talks about animal weapons! Jessi from Animal Wonders joins the show to talk about animal defenses and introduce us to the southern three-banded armadillo.

Link to Doug's book:
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[SciShow Intro Plays]

 Animal Weapons: Antlers

Hank: Hello! Welcome to SciShow talk show, that day on SciShow where we talk to interesting people about interesting things. Today, we have joining us Douglas Emlen, also known as Doug, author of "Animal Weapons", a book about the various arm races that have gone on between all sorts of animals including, turns out, us. Doug, hi!

Doug: Hello. Thanks for having me here.

Hank: How's it going? Yeah, absolutely.

Doug: It's going great.

Hank: So, I love science books and I was excited to find out that there was someone right here in my very small town of Missoula, Montana who had written one. Uh, tell us a little bit first about your research. Who do you research?

Doug: I work on beetles is what it comes down to. And I want to qualify that the book is on animal weapons and I work on animal weapons, but I work on a special subset of weapons which are the really, really big weapons and I just have to confess at the outset, I have been crazy about animals that are so bizarre looking and extreme that when you look at them, they look like they shouldn't be possible.

These are animals that look like they should tip over [Hank laughs] or they should trip or they should get tangled in the trees or the branches when they move, because the things sticking off of their bodies are that extreme and so, in the case of the beetles, there are thousands of species that have horns sticking off the front of their bodies. It can be coming off the thorax or the shoulder blades or coming off the heads. There are species with one horn, two horns, five horns, all sorts of weapons coming off these things and most of my research concerns--

Hank: [takes beetle, mumbles] I want one, so he doesn't have things to grab on to.
Doug: --sort of the genetics and the development and the evolution of these weapons.

Hank: So like why it happens, how it happens?

Doug: You got it, all of it. I started out years ago looking at beetles that were even smaller than these guys, little tiny dung beetles that had crazy horns coming off their bodies and we really didn't know much about what they did so a lot of the research was watching them in the wild and figuring out how they used the horns and they're basically analogous to what you'd see as antlers in elk or deer. The males have the weapons. Females don't. And they use them in these battles over access to females and these things are extreme.

Th-they're expensive to produce, they're awkward and expensive for these guys to carry, they make it more difficult for them to maneuver, to do basically anything. I mean, imagine having an extra leg on your head for everything that you do. It would get in the way all the time, but the ultimate currency that matters in life is reproduction. And they help a lot when it comes to getting access to reproduction. These things tend to crop up in species where there's intense competition among males over access to a limited number of reproductively available females and in those battles, that is literally do or die. If you fail to breed, you're done. I mean, that's it. That's the end of the game in the evolutionary sense. So, so these guys, these weapons matter a lot in competition for reproduction.

Hank: So, this is a big set of, is a big weapon, but it doesn't feel huge to me. I was wondering if you could show me an actual, like, like-

Doug: Put it into context for you?

Hank: Put into context.

Doug: I can do that. Can I get up and go get it?

Hank: Yeah, go get it.

[SciShow Transition]

Doug: We are back on, alright. So, to scale that up to a more appropriate size for us to appreciate, I happen to have a pair of elk antlers. And again, the key point is these antlers, relative to the size of that bull elk, are actually smaller than some of the horns that these beetles produce and carry around on their bodies. And I can promise, and I can give it to you if you want, these things are heavy. I mean, it's - it's incredible to imagine a bull carrying this around, you know, on top of their heads for everything they did!

Hank: That's - that's like as big as they get, right?

Doug: This is a pretty decent sized male. They get a little bit bigger.

Hank: Yeah, because I see - I see elk but I don't see them this far away and so I have a hard time imagining that they really are that big.

Doug: And, they're that expensive. When these weapons get big, they get expensive. They get very, very expensive for these animals to produce and the antlers are a really good example to illustrate that point.

Hank: Well, they do all that work to produce them and they're so energetically expensive to even have, to carry--

Doug: I promise you can just sit here and do your exercises with these things, they weigh a ton.

Hank: I want to. Let me see.

Doug: But, um, not only is it expensive for these animals

Hank: Can I even? Oh my god.

Doug: To carry that everywhere they go

Hank: Hello, buddy.

Doug: but producing

Hank:  Uuuoohh... I'm not a strong man.

Doug: I'll let him hold it.


Doug: It costs a lot for the animals to produce it. There's been some really neat studies looking at how much it costs the males to actually produce that and the most recent estimates suggest it costs a bull elk as much to produce a rack of antlers as much as it costs a cow to raise two calves all the way to weaning. That's a huge investment.

Hank: Oh yeah. You could be

Doug: And one of the ways to appreciate that

Hank: making so many more babies. If you were, if you were sharing that wealth.

Doug: Exactly. Well, no that's the point. They wouldn't be making any babies if they didn't allocate the wealth. And that's a really good place to point out the cost. They're building bone. And they need phosphorus and calcium in order to make the bone and they can't get enough of that from the, the forest they feed on. So some of these studies suggest that these guys--

Hank: Cannibalize from their own bones?

Doug: They do. They shunt it. They leach these things out of the rest of their skeleton to pour it into these weapons. And then they throw their weapons away at the end of the season. So these males actually go through a brittle bone osteoporosis period exactly during the rut, when they need these things and they're smashing into rival males in these knockdown, drag out, do-or-die battles.

And again, elk are sort of an example that we can see and relate to, and because they're heavy it's easy to appreciate how expensive they are, but it's, it's important to recognize that there are all kind of animals that do that, right? So there's rhinoceros beetles, there's dung beetles, there's flies, there's crabs, there's shrimp with huge claws. There're thousands of species out there where the males are doing exactly the same thing. They're shunting huge amounts of resources into these weapons for one purpose. Just to duke it out, fight over access to females.

Hank: But there are, there are other reasons to have weapons. Cause traditionally, we think weapons are for... killing. Uh, and these don't do that much killing, I imagine.

Doug: Nope. Well... no.

Hank: Occasionally. 

Doug: Occasionally. No, that's actually one of the fun twists that came out of reading about these arms races, is one of the things that happens in this kind of a weapon. You've got the very small number of males with the huge weapons, you have lots of the population somewhere in between with sort of intermediate weapons, and you've got the smallest males with the fewest resources and the tiny tiny little weapons. The weapons end up becoming hugely disparate in size from animal to animal within a species within a population. And it makes them a good signal.

Hank: Mhmm

Doug: It's not an accident that the really big, best-conditioned male has the huge weapons. It's because he is in the best condition and the healthiest and the most resistant to parasites and had access to the best food and that's why that male had the really big weapons. That's the male that's gonna win the fight. So if you're a male and you're going up to another male and you gotta decide do I wanna launch into this thing, it makes really good sense to look at the weapons first. But what it means is these males don't actually fight as often as you'd think they would.

Hank: Right. They're just signalling.

Doug: They can fight.

Hank: Right, of course.

Doug: And they will fight.

Hank: I can definitely see...

Doug: But what happens is most of the encounters end up getting resolved without a fight.

Hank: So we have weapons used as a deterrent, as a signal, but then there are also weapons that are developed that are actually used for death and killing.

Doug: There are. 

Hank: And you know, you look at, you look at lions, they got big teeth,

Doug: Yeah.

Hank: But it's not like this, you know, they don't have like teeth sticking out of their face. And they're just not like hitting- cause they gotta be sleek, they gotta be fast...

Doug: Right.

Hank: But there are some animals that have crazy, crazy teeth. And that...

Doug: And I got one of those too.

Hank: Okay, sh- let's talk about that.

 Animal Weapons: Teeth

Hank: Alright, so this is a crazy... set of teeth. I just duh--, like... Why would a predator that has to chase and be, and like, cause we think of tigers, and you know, cats now, it's mostly

Doug: Yep.

Hank: chase-y... uh,

Doug: Yeah. Like a cheetah.

Hank: run-em, run-em-down.

Doug: Run-em-down.

Hank: And that's gonna slow

Doug: Which is

Hank: you down.

Doug: exactly why there aren't very many things out there like this.

Hank: Yeah.

Doug: So this is a really screwed up animal.

Hank: Ha!

Doug: You look at it... everything about these guys is a mess. But, um

Hank: So, they, they actually, their jaws do close. Then you have this happening. [holds up skull] Which is, I mean, it's terrifying, but it's also a little silly.

Doug: So this was a problem for me, right? So here I was, trying to read about all these animals with crazy weapons and most of the weapons that I study, and the...  and the most of the weapons I was reading about, are these weapons that are used by males.

Hank: But it looks like a walrus tusk, which would be used by

Doug: Well, so walrus tusks are used by males. They're sexually dimorphic. They play by the same rules as the beetle horns and the elk antlers. These guys didn't. So there was this problem. It was clear that there were also other examples of really extreme weapons that weren't specific to the males, that weren't used in these battles over access to females, they had- they were used by predators. And you raised the key point there. Why would you ever get an extreme weapon in a predator? Because most predators have to, they have to fly fast, or swim fast, or run fast, they gotta be agile. You picture something like a lynx chasing a snowshoe hare [snaps fingers] they burst out of the prey--, I mean they just explode

Hank: So you have, you have weapons.

Doug: out of their hiding place

Hank: but you have appropriate, efficient weapons.

Doug: Because if they get too big they slow you down. They make you awkward and gangly and you're not gonna catch they prey in the first place. So the bottom line is bigger weapons are better for killing. You can kill bigger prey if you have bigger teeth. But when they get to the point where they make your head all screwed up or the head has to tip back in order to arrange for the teeth you can't catch the prey in the first place.

Hank: Yeah, you've got your eye socket literally is closing cause you have to have the muscles flying through there like that. That is a weird...

Doug: Exactly.

Hank: This is a weird shape for an animal.

Doug: So... so the point is most predators can't play by those rules. They'd never make it. They would starve because they wouldn't be able to catch their prey. And so the trick with these guys is that they're not your normal predator. They were not fast. These are not cheetahs with big teeth. These were big, stocky, robust animals that... they could not have run down anything. But we don't think that that's what they did, so the- the latest palaeontological studies suggest looking at joint- you know, articulation and what these guys have, their muscle size and what they did.

The latest ideas on saber-tooths is that they actually hung out on branches of trees. And they dropped onto unsuspecting prey, like the lumbering juvenile mastodons. Ans they literally dropped from above and plunged the suckers into the back of the neck of their prey. And so they were ambush predators. And that's the ticket. That's the key to understanding weapons like this because an ambush predator doesn't have to run fast. They don't have to stalk and chase down their prey. They sit and they wait and grab it when the prey comes close to them. Or they drop like a cat. But if you think about it, there actually are a lot of predators that are ambush predators and many of them have crazy weapons like that.

Hank: I also want to point out that this is how this thing's jaw actually hinges. To get it open enough to get these...

Doug: So the way I like to explain that is it's like opening up a stapler. If you wanna use a stapler where you punch it down into paper you have to flip open the bottom hinge. 

Hank: It's got an extra hinge.

Doug: To flip the bottom all the way out of the way because it's the only way you can bring it into contact. And that's why these guys have a special hinging mechanism that lets their jaw fold all the way back so that they could use those things. And if you look at it when they close their jaw- I mean these were really screwed-up animals. Their heads were tilted back in order to project the jaws forward so they couldn't see where they were running. And they- these things got in the way- imagine eating with teeth like that.

Hank: Yeah.

Doug: I mean think about it. So, so the wear patterns on the teeth suggest that these guys had to gnaw their food through the sides of their mouths, because there was no way to get around the giant teeth! So they could kill something, but once they had it what're you gonna do? Basically they had to eat sideways through their mouths to get past these things. And so the idea there is that normally predators face sort of a tug-of-war balance. Killing bigger prey means you want bigger jaws, bigger mouths, bigger teeth- but it slows you down. So if you have to catch the prey there's this balance. Selection for maneuverability

Hank: There's also

Doug: keeps the weapon small, selection for killing keeps it big. Once you're an ambush predator, that constraints gone.

Hank: All you need is

Doug: Off to the races.

Hank: big, big weapon.

Doug: Yeah, really big jaws.

Hank: Alright, I am fascinated. This, this is Douglas, Douglas Emlen's book Animal Weapons. You can get it, um, wherever books are sold

Doug: Hopefully.

Hank: Um, so: If I was an animal that had to worry about ambush predators, which thankfully I no longer am, what kind of strategies would I be hoping for?

Doug: I know what I'd want.

Hank: Yeah.

Doug: That'd be a really good suit of armor.

Hank: Alright. Uh, Jessi is going to join us with an animal that has a really good suit of armor.

Doug: Exactly.

 Creature: Armor

Hank: Alright everybody, this is Jessi Knudsen Castaneda from Animal Wonders, and she has a present for us. It's wrapped up.

Jessi: It is like a present, yeah. Well she's sleeping and she can get cold easily- and it's wintertime now. So I wanted to make sure that she stayed nice and warm. But.. here she is.

Hank: There's a soft ball. There's a soft ball in here.

Jessi: This is a southern three-banded armadillo. And she's got a heck of  a set of armor there.

Doug: Yeah. That's amazing.

Jessi: Yeah.

Doug: This is a dream come true. Can I hold it?

Jessi: Uh-huh ha ha.

Doug: Please?

Jessi: In a second.

Doug: Please? 

Jessi: In a second. Yeah, well, you touch her and then I'll let you hold her in a second.

Doug: I've always wanted to see an armadillo

Jessi: Cause she'll roll up into a ball

Doug: That's okay.

Jessi: if she smells someone unfamiliar.

Doug: So most of the animals with armor do that, right?

Jessi: Exactly. Exactly. So that's her 

Doug: Armadillos, trilobites do that. Pill-bugs do that.

Jessi: Yeah, they have the same, same type of mechanism that's allowing them to survive over and over, is that they will, if they are threatened, they will roll right up into a ball.

Hank: Aw, scared.

Jessi: She can roll...

Doug: Aw, man, that's--, that is so cool

Jessi: completely up... into a ball.

Hank: And the tail makes like the other piece that the head...

Jessi: Yeah! She's like a little puzzle.

Hank: Perfect.

Jessi: Yeah!

Doug: Little jigsaw puzzle.

Jessi: Yeah.

Hank: Oh man. Aw.

Jessi: Little hat piece there.

Hank: Aw. Yeah. I'm sorry.

Jessi: Are you coming back out there?

Hank: Where did this little girl come from?

Jessi: She was, um, purchased to be a mascot for the World Cup.

Hank: Well that's weird.

Jessi: And, um to bring in, you know, people, to come, you know, "Woo! We have our own armadillo!" Cause the mascot for the World Cup was the Brazilian three-banded armadillo, and they raised funds to, to help out with the endangered species and conservation. Um, but these guys look very similar to the three-banded- the Brazilian three-banded. And so she was purchased for that, and then when the world cup was over- no use for her any more, and so she was sent to a rescue and we rescued her from there.

Hank: Was it- was it like a bar, or something wanted to have it? Or what, like, who...

Jessi: I don't, I don't know exactly who the people were.

Hank: Cause like, "Come on in to get, uh, to get

Jessi: "See the armadillo!"

Hank: "Armadillo. Buy beer..."

Jessi: Yeah.

Hank: "and watch the World Cup."

Jessi: Yeah. And drink. Yeah.

Hank: Yeah.

Jessi: I'm not sure, but... but then she lost her home, and

Hank: Now I have a new one.

Jessi: Now she has a new one.

Hank: Well good, I'm glad.

Jessi: You know, she does not have a name. We've been calling her "her" and "armadillo". She does not have a name. She's a new ambassador and we're actually looking for someone to name her...

Hank: Oh.

Jessi: For a donation.

Hank: Oh, yes. 

Jessi: You know, they can, they can, they can name this little lady right here.

Hank: Adopt an armadillo.

Jessi: Exactly.

Hank: You're weird. No offense.

Jessi: She's really weird. [Hank imitates an armadillo.] She's really weird. And she, I think the weirdest part of her is how she moves around.

Hank: Especially now that she's ice skating. [The armadillo is walking on the table]

Jessi: She is. She is. It's very hard for her to

Hank: Yeah, it's like she's got ice skates on the front.

Jessi: She just keeps her front feet like this [points] and then she pushes around with her back.

Hank: It's like you have just one fingernail... I wanna see her belly, but I feel like it's unlikely.

Jessi: You can. You might get a- if I open her up

Hank: I might get a glimpse.

Jessi: and just get her calm and then... [holds it up]

Hank: Oh, it's so fuzzy.

Jessi: Yeah.

Hank: Oh, okay... oh, she's like, "I don't

Jessi: She's like "I don't like this. No thanks."

Hank: "I don't like this. I don't like it."

Jessi: Yeah. And I was having a blanket on her. I keep trying to put my hand on her like this and keep her on my lap- make sure she stays warm, because these guys, um, are very susceptible to cold. And they have a pretty low basal temperature and metabolic rate. They're low, just like humans, and so they can actually get leprosy. And everyone knows that. Everyone knows that

Hank: Right.

Jessi: At least most people do.

Hank: What leprosy thing?

Doug: You didn't tell us.

Hank: Am I- am I- should I not lick my hands? So they can get leprosy...

Jessi: Can you get leprosy?

Hank: NO. I- I'm. Can I? Sure.

Jessi: Mmhm. I can get leprosy. Humans can get leprosy.

Hank: Everybody can get leprosy.

Jessi: Armadillos can get leprosy.

Doug: Right, but you didn't tell me that before this interview.

Hank: Fine, but most animals can't.

Jessi: Most- most animals- most mammals, most placental mammals can't because they have a higher body temperature.

Hank: Oh.

Jessi: And it'll kill it off. But the ones that have lower, are able, are susceptible to it. And she doesn't. I mean, she's been tested and just like

Hank: She doesn't have it. That's nice.

Jessi: we would know. We would know if we had leprosy.

Hank: Right.

Jessi: Yeah.

Hank: Yeah. Well

Jessi: And it could be treated. It's treatable now.

Hank: In armadillos as well as humans?

Jessi: Yeah. Yeah. Yep.

Hank: Okay.

Jessi: Yeah.

Hank: That's nice to know.

Jessi: Yeah.

Hank: I don't know very much about leprosy. I should do a SciShow on it.

Jessi: You could do a SciShow on leprosy. That'd be an upbeat one.

Hank: Yeah. Not... yeah. But there're always, yeah, are people always like, "Don't touch armadillos, they'll give you leprosy." But really what it is is that they are capable of getting leprosy and carrying it. Alright. Well. This unnamed animal which you can name if you go to and check out the Animal Wonders campaign, uh, you can adopt an armadillo.

You can also get Douglas's, uh, Douglas Emlen's book, Animal Weapons, on Amazon or I could talk about this stuff with you for hours, and I want to, um, but luckily, for everyone else, you can just read the book, and it'd be like talking to him for hours. Um, so that's- got a link in the description for that.

Uh, and you can check out Animal Wonder's web- uh, YouTube channel at So thanks so much for bringing in so thanks so much for bringing in this unnamed, beautiful beast.

Doug: Soon to be named.

Hank: Uh, and it was just an absolute pleasure to talk with you, Douglas. 

Doug: Pleasure.

Hank: This has been an episode of SciShow Talk Show that I have really enjoyed. Thank you for joining us, if you want to keep getting smarter with us here at SciShow, you can go and subscribe.