
Written by a model from the transcript; not yet reviewed.
The episode explores the prehistoric Carboniferous period, when Earth was dominated by giant insects like suitcase-sized dragonflies and two-meter-long millipedes, and investigates the long-standing mystery of why these massive bugs eventually died out. The guest and host examine the classic scientific hypothesis that higher atmospheric oxygen levels allowed ancient insects to grow so large, contrasting it with new experimental physiology research questioning whether oxygen availability actually limits insect body size. Listeners are guided through wind tunnel experiments on locusts, muscle dissections across dozens of insect species, and alternative theories involving predation by flying dinosaurs and climate change, revealing that insect biology remains surprisingly mysterious.
The host promotes Sonos, describing its sound system and app features.
A brief ad for Google Gemini, highlighting its image recognition and AI capabilities.
The hosts explain the Carboniferous period, its timing, and its swampy, fern-filled environment.
Discussion of the massive dragonfly-like insects and millipede-like bugs that existed during this era.
The hypothesis that higher atmospheric oxygen allowed insects to grow larger is introduced.
Ned Snelling’s work on insect metabolism and oxygen delivery is described, challenging the oxygen hypothesis.
Explanation of how insects breathe through spiracles and tracheal tubes, contrasting with human respiration.
Exploration of how oxygen diffusion limits insect size and the debate over whether higher oxygen levels enabled giant bugs.
Hosts connect past bug size trends to modern insect population declines and the need for further research.
Study of how oxygen tube space scales with bug size, revealing only modest increases for much larger insects.
Discussion of environmental changes, predation, and other factors that may have caused the disappearance of giant bugs.
The episode ends with acknowledgments, sponsor messages, and a call for listener feedback.
Suitcase-Sized Prehistoric Dragonfliesstory
The host describes the astonishing scale of Carboniferous insects, noting fossil evidence of carnivorous dragonflies with a 70-centimeter wingspan.
Higher Ancient Oxygen Levelsdata
The host and guest explain the standard theory that ancient oxygen levels were around 30 to 35 percent compared to today's 21 percent.
How Insects Breathe Through Spiraclesinsight
Experimental physiologist Ned Snelling explains that insects breathe through small ports called spiracles on the sides of their bodies instead of using lungs.
Locust Flight Chamber Experimentstory
Researchers tested insect oxygen consumption by flying locusts inside a mini-flight chamber resembling a tiny wind tunnel.
Tiny Oxygen Investment in Musclesdata
While human hearts dedicate about 10 percent of muscle space to blood vessels, locust flight muscles dedicate less than one percent to oxygen tubes.
Minimal Oxygen Scaling in Big Bugsinsight
A study of 44 insect species showed that a bug 10,000 times larger than another only needs marginally more space for oxygen tubes.
Alternative Evolution and Predation Theorydebate
Researchers suggest that the evolution of other flying predators during dinosaur times made larger insects much easier targets to hunt.
“So I want an amazing sound system. But I also want something that's easy. It just works.”
“They think the Carboniferous was more like 30% to 35% oxygen.”
“But if in this experiment, the insect had no issues getting oxygen to its cells, right?”
“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.”
Once upon a time (around 300 million years ago), Earth was home to massive dragonfly-like insects and two meter long millipede-like creatures. Why did they die off? Guests: Ned Snelling, professor of experimental physiology at the University of Pretoria; Jon Harrison, professor of environmental physiology at Arizona State University For show transcripts, go to vox.com/unxtranscripts For more, go to vox.com/unexplainable And please email us! [email protected] We read every email. Support Unexplainable (and get ad-free episodes) by becoming a Vox Member today: vox.com/members Learn more about your ad choices. Visit podcastchoices.com/adchoices
4,423 words · 10 speakers
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