What happened to the giant bugs?

8:29Jon Harrison:so i guess if there's like more oxygen in the atmosphere it's it's it's like they're they're just in more oxygen and more oxygen will passively diffuse into their body and let them get

8:40Ned Snelling:bigger right the idea is the the bigger you get the sort of further oxygen would need to go um and so if you're you're too big the idea is that maybe oxygen wouldn't get to your really

8:51Jon Harrison:really internal bits but if there's a lot of oxygen yeah okay right maybe it's just it's

8:57Ned Snelling:more likely some oxygen gets all the way down in the tube and so you can grow bigger.

9:03Jon Harrison:That makes sense. Yeah. You're going to tell me that that's wrong.

9:06Ned Snelling:Well, so like this idea that tubes limit insect body size goes back a long ways, right? In 1995, it's a pretty important hypothesis that's published in the journal Nature around this. It points to some research suggesting there was lots of oxygen in the carboniferous, right? And talks about how that oxygen might have affected life forms at the time. And in the paper, they talk specifically about, like, the big dragonfly guys. And they're like, flight requires so much energy, so much oxygen. In order for flight to be possible in big insects, they just need more oxygen in the air. Even if they have air pumps, whatever, in a system that relies on diffusion, just need more oxygen.

9:45Ned Snelling:Less oxygen, no big bugs. That's the explanation. I was taught a version of it. It sounds super plausible. But Ned just did a bunch of research and published a paper in Nature arguing that it might not be right after all. Huh. And why? I'll tell you what we know.

10:12Jon Harrison:No, no, no. Don't tell me after the— Ah!

10:20Jon Harrison:Support for the show comes from Sonos. Hey Sonos, give me some music. All right, one of life's great mysteries. You're listening to music in the living room, but you gotta grab something from the kitchen. You don't wanna take the speaker with you, but you also don't wanna miss that beat drop. And this is where I introduce you to the magic of Sonos. Sonos sent me a couple speakers to try out, so I've gotta move to here in the living room. And then I walk down the hall.

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11:09And yeah, I didn't miss a second.

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12:00Ned Snelling:Support for the show comes from Square, the business platform that aims to help sellers become neighborhood favorites. These days, buying stuff is pretty easy with Tap to Pay. Maybe it's a breakfast sandwich at the corner cafe, a lunch break haircut, or some wall art that you picked up spontaneously on your way home. Square says every day we interact with businesses that rely on Square to make those transactions so fast and so simple. Square brings payments, point of sales, inventory, staffing, and online sales together in one easy-to-use system. Their hardware is sleek, simple, it comes with software that's intuitive to use in your day-to-day operations, and it also has AI-powered tools that help automate routine tasks, giving you more time back as a seller.

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14:19Ned Snelling:Ned says he actually started to question things years ago when he was looking at the oxygen architecture of bugs, essentially. So these tubes and their evolution and their design.

14:32Jon Harrison:One of the experiments I did was I flew locusts in a mini flight chamber to measure their oxygen consumption rate. Hold on. Before you explain this experiment, what is a mini flight chamber? Yeah. Do you know what this looks like?

14:50Ned Snelling:It's like a tiny wind tunnel. Okay. So I was picturing an F1 wind tunnel. Of course. And he basically said, no.

15:00Jon Harrison:I probably wouldn't describe my flight chamber as Formula One. It was a bit more rudimentary, but thanks for the compliment.

15:08Ned Snelling:You told me to picture a little cylinder with air flowing through it and then a locust flying inside it.

15:16Jon Harrison:I'm imagining like an air treadmill, like air blowing one way and the locust kind of flying against it. So it's just sort of flying in place while the air is.

15:26Ned Snelling:Yeah, that's what I'm picturing. That's just crazy. He was able to, like, measure the air on the back end also, or, like, properties of the air on the back end. And what surprised him in this research was that the locust did not seem winded by the—oh, no pun intended. But, like, the locust didn't seem winded by their exercise. So if humans went for a run, especially if that run was quite energy intensive,

15:56Jon Harrison:say we were sprinting for a period of time, after we finished exercising, our oxygen consumption rate would remain elevated. We would pant.

16:06Ned Snelling:We stop running and we just go like... And by we, I mean me. Sam. No, Bergman, I run a mile. I don't pant at all. But so his locusts, they did not seem to do like the locust version of panting.

16:26Jon Harrison:They recovered from exercise immediately. And so what that told me, or at least indicated to me, made me suspicious, was that, hey, this insect has no problem getting oxygen to its cells. It's so good at getting oxygen to its cells that even after flight, which is the most energy-intense form of exercise, even after that, it recovers almost immediately. And so he was like, that's weird.

16:59Ned Snelling:The whole basis for sort of thinking that oxygen levels killed off massive dragonflies was insects supposedly are less efficient at getting oxygen to parts of their body than we are. They need more oxygen in the atmosphere in order to get big because they have this passive breathing or whatever. But if in this experiment the insect had no issues getting oxygen to its cells, right, if it's not even panting after exercise, it does raise the question of are they actually inefficient at getting oxygen?

17:33Jon Harrison:Yeah.

17:33Ned Snelling:So to investigate this a little bit more, Ned wound up cutting up locust flight muscles to just look at them more closely. Like in the wings? Yes. So the mussels that power the wings. Imagine a mussel like this is like a city, right? Every day that city sort of needs to be supplied with food. It's like the mussel needs oxygen. So the city has trains coming in to deliver supplies. And if the trains are really fast and can just carry huge amounts of supplies, right, If they're true freight trains and this is a really efficient system, maybe you can have just one track come into the city and that'll supply the city with everything that it needs, right?

18:24Jon Harrison:High speed rail.

18:25Ned Snelling:But if your trains are not great at carrying supplies, they're just kind of slow, low capacity.

18:32Jon Harrison:More of the choo-choo variety.

18:34Ned Snelling:Yeah, they're choo-choo trains. Maybe you need a lot of train tracks coming in to make sure that you have enough supplies for the city, right? Maybe you need actually a pretty big percentage of your city just to be given over to trains and train tracks.

18:48Jon Harrison:Yeah.

18:48Ned Snelling:So basically, looking at these flight muscles, Ned wanted to see how much space in the muscle was given over to train tracks coming in, to sort of these oxygen tubes bringing in oxygen. Got it. And for comparison, our hearts, they have pretty active muscles because they're beating all the time. And there's some different numbers here, but Ned was telling me that something like 10 % of the space in our heart muscles is just blood vessels, just trains carrying in supplies. When he looked at the locus flight muscles, he found that less than 1 % of the flight muscles were given over to, in their case, oxygen supply tubes.

19:34Jon Harrison:That's a very small percentage of the flight muscle dedicated to these oxygen supply structures.

19:43Ned Snelling:So yeah, you would think that locusts would require lots of train tracks to supply the city with oxygen, that they would not be so efficient. But that's not the case.

19:55Jon Harrison:Yeah. That being said, this is just one bug, right?

19:59Ned Snelling:Who knows if it's going to hold up for other bugs? Ned knows. Because several years later, he, you know, he was still intrigued by this idea. And he wanted to look at several insects, but specifically he wanted to look at the flight muscles of really small flying insects and the flight muscles of really big flying insects and everything in between. to see as you go up in size, does something change? Like even if bugs are very efficient, it still could be at a larger size,

20:39Jon Harrison:this still could be the reason why they're struggling.

20:42Ned Snelling:Exactly. So he works at the University of Pretoria in South Africa. There are lots of big bugs around, apparently, like the goliath beetle, which, as you can imagine from its name, is big.

20:57Jon Harrison:It's not quite the size of a baseball. And if I placed one on the palm of your hand, you wouldn't be able to see the palm of your hand. Oh, God. That's... So it's big. Really big. I just, like, don't... I don't love bugs. Okay, well, you've come to the wrong place. I mean, I do want to know. I want to know what happened to the bugs.

21:22Ned Snelling:So basically, he's running around his campus. He's trying to catch insects of different sizes.

21:27Jon Harrison:To say that caused some interest in colleagues and students would be an understatement. I had students directing me to different vegetation where I could find different types of insects, particularly large species of insect. So that was a big help. Just imagining this professor running around just trying to catch bugs. I love it.

21:50Ned Snelling:And he was just trying to get as much sort of diversity in sizes as possible. And so in the end, he got 44 kinds of insects, a whole range of sizes, dissected them to get their flight muscles, did a comparison, and basically wanted to see, like, was there a relationship between how big the insect was and sort of how much of its flight muscles were devoted to oxygen delivery? Were these cities overrun with train tracks as the insects went up in size, or did the number of train tracks remain relatively consistent?

22:28Jon Harrison:Did it just stay as like one high-speed rail going into the city?

22:30Ned Snelling:And the answer was that, yes, bigger bugs did need a little more space for oxygen tubes.

22:39Jon Harrison:Okay.

22:39Ned Snelling:But not dramatically more space. A bug could actually be 10 ,000 times bigger than another bug and only need sort of a tiny bit more oxygen tube space in its flight muscles.

22:55Jon Harrison:Wow, so it really might not be the oxygen then.

22:59Ned Snelling:Well, that's why Ned is sort of skeptical.

23:03Jon Harrison:Yeah.

23:04Ned Snelling:He thinks this study shows that we need to find a different explanation for what killed them off. I did talk to a researcher who suggested that it could have been an environmental issue. So as you're transitioning from the Carboniferous into the Permian, the world is changing a lot. Things got hotter, drier on Earth. And with that just comes size reduction in animals.

23:31Jon Harrison:We're seeing that with the shrinking birds and climate change. Yeah.

23:36Ned Snelling:And then another guy said, you know, big animals in general, they're just fewer of them. They're rarer. And so it's easier to kill all of them off. It's just less likely that at least one of them survives. And then a study from 2012 looked at a later moment when there was actually a lot of oxygen in the air, but other things had evolved to fly around. So this was sort of later in dinosaur times. And it showed that insects actually got smaller then, which suggests that maybe insects have a hard time being big when there are just sort of other things in the air to take them out. So that might be the thing that's more affecting their body size is if there are things that can hunt you that can also fly and you're bigger, you're just easier to hunt.

24:30Jon Harrison:Yeah, it feels easier to catch a suitcase-sized dragonfly than a tiny little one zipping around. Sure.

24:38Ned Snelling:But all that being said, there is also still the possibility that we should not throw the oxygen idea out entirely. So, as he was doing all this work, Ned ended up connecting with this environmental physiologist whose whole focus is insects. His name is John Harrison. And he has actually been skeptical of the too little oxygen killed off the big bugs hypothesis since at least the 90s.

25:11Jon Harrison:An OG oxygen skeptic. I thought, well, that would probably just take a year or two to disprove.

25:17Ned Snelling:30 years later, he is still not sure that they have all the evidence they need to declare it wrong, necessarily. So he ended up working with Ned so much on all of this that he was listed as a co-author on this paper. But he's cautious still because he thinks that stuff like molting might be expected by oxygen levels. And he also thinks that, like in this paper, they've shown that flight muscles don't depend on this oxygen stuff so much. But other tissues that are further off in the body or less well supplied, he thinks those tissues might still have an issue.

25:56Jon Harrison:You know, the legs, the muscles in the legs may be harder to ventilate than the flight muscles, which can be maybe really easily ventilated. So that's a possibility.

26:07Ned Snelling:He and Ned don't totally agree on this point. Ned feels like they've addressed this in the paper, but John does not think that they have a final answer yet.

26:16Jon Harrison:I do think we've made a lot of progress, but yeah, I don't think it's definitive yet in my own mind. The murderer is still at large.

26:26Ned Snelling:I will say, though, that one thing Ned and John agreed on is that it's just hard to understand bugs in general. John was telling me that there are still questions about their breathing, for example. And then Ned was talking about the questions we have about the insect die-offs we're currently seeing. So we did an episode a while back where we talked about how we are losing a lot of insects, but people are struggling to work out how many insects we're losing, why that's happening. And this is currently, you know, not 300 million years ago, but in the 21st century. And we still have a lot of questions around it.

27:09Jon Harrison:Perhaps if we are able to work out what's caused a decline in the size of insects prehistorically, it also might help us to try and work out what is causing insects to decline currently. because at the moment, we really don't have a good idea of really what's causing that. You know, if we understand what happened prehistorically, it might actually help us to try and tease apart and work out what's happening or what's not happening at the moment. Oh, that's so interesting.

27:45Ned Snelling:Okay, bug time is over. Thank you.

27:48Jon Harrison:No more imagining handfuls of beetles.

27:59Ned Snelling:This episode was produced by me, Bird Pinkerton. It was edited by Joanna Solitaroff and Meredith Hodnot. Meredith runs the show, and Joanna is the editorial director. Christian Ayala did the mixing and the sound design. Melissa Hirsch checked the facts. Noam Hassenfeld does our music. Valerie Schenkman, Jake Reynolds, and Kareem Correa are the fact that houseflies do something like tasting with their feet. And thank you always to Brian Resnick for co-creating the show with me and Noam. Huge thanks also to John and Ned for being so generous with their time. And to Conrad Lavendera for talking me through questions of insect gigantism.

28:39Ned Snelling:If you have thoughts about bugs or honestly thoughts about anything at all, please reach out at unexplainable at Vox.com. We love to hear from researchers about what they're working on, from people who have questions they'd like us to unexplain. unexplainable at Vox.com. If you would like to support the show, I cannot tell you how much it would mean to us if you would become a member of Vox. It is very easy to do. Just go to Vox.com slash members and you'll get access to all of Vox's journalism, but you'll also know that you are supporting all of Vox's journalism. And for those of you who have emailed us to let us know that you signed up because of Unexplainable, you're the best and you're right up there.

29:22Ned Snelling:with the people who also have left us nice reviews or the people who have told people in their life about the show. Unexplainable is part of the Vox Media Podcast Network, and we will be back very soon with another episode about everything that we do not know.

29:53Ned Snelling:Support for the show comes from Injun. Running a small business means every dollar has to work hard. But if your team is still booking travel the old way, it's costing you more than you think. Injun is the fastest growing travel and spend platform in the country, built specifically for businesses like yours. Book a trip in as little as two and a half minutes. Earn up to 10 % back on hotels. And in 2025, Injun customers saved more than$300 million on travel. with zero booking fees, no contracts, and no BS. More than 1 ,000 businesses join Engine every month. Join them and get$500 when your business signs up and starts traveling at engine.com slash Vox.

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