The horn of the Japanese rhinoceros beetle can grow to be two-thirds the length of the rest of its body. And size matters. The beetles battle with their horns to get access to female beetles. Biologists Doug Emlen and Erin McCullough, of The University of Montana, are looking into what regulates the size of this extra-large attribute.
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IRA FLATOW, HOST:
Flora Lichtman is here with our Video Pick of the Week. Hi, Flora.
FLORA LICHTMAN, BYLINE: Hi, Ira.
FLATOW: What you got for us this week?
LICHTMAN: This week's video pick is about a very menacing creature, and I want to give our listeners a chance to guess what it is based on some clues from University of Montana, biologist Doug Emlen and Erin McCullough.
ERIN MCCULLOUGH: These males have a giant pitchfork sticking out of their forehead.
DOUG EMLEN: These are among the largest outgrowths of any kind of weapon that you see in any animals.
MCCULLOUGH: You can definitely watch intense fights for hours.
LICHTMAN: Well, at least minutes on our website.
FLATOW: A giant pitchfork...
FLATOW: ...sticking out of their heads, intense fight.
LICHTMAN: Intense fights. And you already know what it is because you've seen the video, and entomologists might know what it is too. We're talking about rhinoceros beetles.
FLATOW: Of course...
LICHTMAN: Of course.
FLATOW: ...rhinoceros beetles.
LICHTMAN: And they live a really intensely dramatic life, I would say. So let me just set the scene for you. They have these huge horns, right? And they use them to pry off their - only the males who have them - pry off other males from the feeding sites.
FLATOW: So they're fighting with other males.
LICHTMAN: Yeah. They're like crowbars, and they just, like, knock other males off of trees. So they're at these trees. They're eating sap. And there's more than kind of like a snack at stake here because that's where they mate with females, at these feedings sites. So like everyone knows and these beetles especially, size matters.
FLATOW: Right, right.
LICHTMAN: Well, right? Like the bigger horn, in this case literally, the more female beetles they'll probably be able to mate with. And so one of the questions that evolutionary biologists and biologists are interested in is what makes a horn big, and what stops it from getting even bigger?
LICHTMAN: Because if the bigger-horned males do better, then what keeps them from just getting bigger and bigger and bigger and bigger? And these horns are about two-thirds the length of their body.
FLATOW: Wow. Wow.
LICHTMAN: So that's a bit the question of the Video Pick of the Week.
FLATOW: Right, that's the question. There's something on our website, @sciencefriday.com. If you want to see beetle battles, this beetle fights there. They're tremendous.
LICHTMAN: Actually, we have like...
FLATOW: And they're tremendous beetles, aren't they.
LICHTMAN: It's like WWF of the insects' world. It's really awesome.
FLATOW: And they're fighting each other on these branches. And, in fact, on the video, you could see - if they get too long, they break off, right?
LICHTMAN: Well, so this is the thing. So this is what Doug Emlen and Erin McCullough have looked into, what is the thing that limits the size? And traditionally, biologists think of cost, like it's hard to fight. By the way, these beetles can also fly.
LICHTMAN: Who would have thought? Or maybe it takes too much energy. And they found out that this wasn't - this doesn't seemed to be the case. But if they get too long, they start to snap. And so, of course, that's no good. And then they've also looked into what gives some beetles longer horns and others don't, and it's diet. You know, the well-fed ones get the bigger horns that you...
FLATOW: Wow. Yeah, it makes sense.
LICHTMAN: Yeah, it makes sense.
FLATOW: Yeah. So if you want to see the battling beetles...
LICHTMAN: Battling beetles on our website.
FLATOW: Our website, @sciencefriday.com. It's our Video Pick of the Week, which also you get it down on our iTunes or iPod subscription. You can see that and...
LICHTMAN: Yeah. I mean, you know, people think of like BBC wildlife, you know, like lions attacking gazelles. You just go watch this video.
FLATOW: Yeah. This is great, better...
LICHTMAN: This holds the - hold their - they hold their own, these beetles.
FLATOW: Better than your shark week.
FLATOW: Let me tell you, you don't know these are beetles. They fight and then you said they can go on for hours, like, you know...
LICHTMAN: Hours, minutes on our website.
FLATOW: Minutes on our website. Thank you, Flora.
LICHTMAN: Thanks, Ira.
FLATOW: Flora Lichtman is our - on our Video Pick of the Week. That's about all the time we have for today. Transcript provided by NPR, Copyright NPR.