Radiolab
Radiolab

Return of the Flesh-Eaters

March 13, 2026

AI Summary

5 min read

In 2016, volunteers in the Florida Keys noticed something grisly: key deer, the tiny, beloved animals that wait at bus stops and let people feed them, were walking around with wounds so deep you could see bone. The culprit was a parasite most Americans have never heard of—the New World screwworm, a flesh-eating maggot that had been officially eradicated from the United States decades earlier. The story of how that eradication happened, and why the screwworm is now marching back toward the U.S. border, is one of the most ambitious environmental interventions humanity has ever attempted—and it raises a question that is as uncomfortable as it is profound: would it ever be okay to deliberately drive a species to extinction?

The Worst Parasite on Earth

The New World screwworm is not a worm but the larval stage of a fly. As journalist Sarah Zhang explains, the female fly lays roughly 400 eggs at a time into any small wound on a warm-blooded animal—even something as minor as a tick bite. The maggots that hatch have two sharp teeth and a ridge on their body that resembles a screw thread, which they use to twist themselves deeper into the flesh. They eat the living tissue, and they are extremely difficult to remove. Science writer Sam Kean, who has also fallen into what he calls the "screwworm hole," describes them as "the worst imaginable parasite on earth."

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What you'll learn

  • 1 Return of the Flesh-Eaters
  • 2 (01:35) **Introducing the Key Deer Mystery** - Sarah Zhang noticed strange, grisly wounds on endangered Key deer in Florida in 2016
  • 3 (03:29) **The Forgotten Parasite** - Screwworm was eradicated from the US, leading to a story about one of humanity's biggest environmental interventions
  • 4 (04:39) **Meet the Screwworm** - Science writer Sam Kean describes the "worst parasite on earth"
  • 5 (05:24) **Edward Nippling's Origin Story** - Born on a Texas farm in 1909, Nippling had the worst job: picking screwworms out of cattle with a screwdriver
  • 6 (09:26) **The Big Idea** - Watching screwworms mate, Nippling learned females only mate once
  • 7 (11:34) **Clandestine Experiments** - Nippling snuck screwworms into a military hospital to use X-ray machines at night

+ Full timestamped outline available in the app

Show Notes

If a species is horrible enough, do we have the right to kill it forever?

Seventy years ago, a nightmare parasite feasted on the live flesh of warm-blooded creatures in North America: the screwworm. That is, until a young scientist named Edward F. Knipling discovered a crucial screwworm weakness and hatched a sweeping project to wipe them out. Knipling’s seemingly zany plan to spray screwworms out of planes all over the continent— with US taxpayer money— succeeded, becoming one of humanity’s biggest environmental interventions ever. 

Today, screwworms have been gone so long that none of us in North America even remember them. But now, they’re coming back. And they’re forcing us to ask: in an era of climate change and rapid mass extinction— should we kill off a species on purpose? 

Special thanks to James P. Collins, Max Scott, Amy Murillo, Daniel Griffin, Phil Kaufman, Katie Barnhill, Arthur Caplan, Ron Sandler, Yasha Rohwer, Aaron Keefe, Gwendolyn Bogard, Maria Sabate, Meredith Asbury, and Joanne Padrón Carney

EPISODE CREDITS: 
Reported by - Sarah Qari
with help from - Latif Nasser
Produced by - Sarah Qari
Sound design contributed by - Sarah Qari
Fact-checking by - Emily Krieger

EPISODE CITATIONS:

**The latest information on screwworm outbreaks and precautions: 
screwworm.gov

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