Radiolab – "Return of the Flesh-Eaters" (March 13, 2026)

Episode Overview

In this episode of Radiolab, hosted by Latif Nasser with producer Sara Khari, the team takes listeners on a deep dive into the bizarre and haunting story of the New World screwworm—a flesh-eating fly whose eradication once marked a landmark scientific intervention but has now made a concerning comeback. The episode blends scientific history, current events, and bioethics, posing one of the thorniest questions in conservation and human intervention: is it ever justifiable to drive a species to extinction?

Key Discussion Points & Insights

1. The Screwworm Crisis Returns

• Background: In 2016, the Florida Keys saw a mysterious outbreak of gruesome wounds on its endangered key deer population.
  • Sarah Zhang: “People suddenly started noticing all these, like, ugly, like, gristly wounds on these deer.” [02:48]
  • Sara Khari: "Gaping holes or wounds in their neck... you could see down to the bone." [02:53]
• The culprit: The New World screwworm fly—once eradicated from the U.S.—laid its flesh-eating larvae in open wounds, causing severe suffering and death in wildlife and livestock.
• This event rekindles public health fears and scientific debates about eradicating dangerous species.

2. The Science and History of Screwworm Eradication

The Screwworm's Life and Impact

• Sarah Zhang describes the screwworm as a fly, whose larvae (maggots) burrow into flesh with "a horrifying mouth... twist themselves down... and eat the flesh." [07:14]
• Historically, screwworms devastated ranchers and livestock in the southern U.S., causing huge economic losses.

The Genius of Edward F. Knipling

• Edward F. Knipling (entomologist) grew up battling screwworms as a farm chore— fueling a lifelong quest to stop them.
  • "Screwworms used to strike fear in the hearts of ranchers all throughout the Southern United States." [06:31]
• Key innovation: Realizing female screwworms only mate once, Knipling hypothesized releasing sterile males en masse could crash the population.
  • Sara: "If he could just make the males sterile... and trick the female screwworms into mating with these sterile males, the females aren’t going to lay any eggs that are viable." [10:33]
• Early attempts involved surreptitiously irradiating screwworms in military hospital X-ray machines to create sterile males. Initial field tests failed on Florida’s Sanibel Island but succeeded spectacularly after scaling up production in Curaçao with insect "factories." [13:08–16:02]
• The approach spread from Florida, across the southern U.S., and through vast international collaboration, eventually eradicating screwworm from all of North America by 2006.
  • "And in 2006, all of North America is declared screwworm free." [19:10]

Maintenance & Economic Impact

• Maintenance: Ongoing “sterile insect barrier” at the Panama–Colombia border costs only $15 million/year, saving over $1 billion in agricultural losses each year. [20:06–20:27]

3. The 2020s Outbreak: Screwworms Return North

The Current Outbreak

• In 2023, Panama saw a dramatic spike in screwworm cases, increasing from 25 per year to thousands—eventually spreading through Central America and encroaching on the U.S. border. [25:05–25:40]
• Theories for resurgence: decreased effectiveness of sterile flies, COVID-related disruptions, cattle smuggling, and global interconnectedness allowing reintroduction from South America. [25:51–26:27]
  • "It's not a matter of if the deadly pest gets to the US, but when." [26:34]
• Governments respond: The USDA and CDC reinvest heavily, establishing new fly factories and border surveillance measures, preparing to release up to 500 million sterile flies per week. [27:13–27:48]

Human Dimension & Public Health Concerns

• The screwworm is not just a livestock threat; outbreaks now affect wild animals, pets, and humans—“over 1000 human cases, and the number continues to grow daily.” [29:48]
• Megan Nichols (CDC): “They are often attracted to mucous membranes. So eyes, nose, ears, urogenital… a patient was holding a bowl in which they were basically sneezing out and pushing out larvae from their nasal passage.” [29:30–30:22]

4. Ethics of Eradication: Should We Drive a Species to Extinction?

The Gene Drive Debate

• Scientists are exploring gene editing (“gene drive”) to wipe out screwworms permanently—potentially “extincting them off the face of the planet forever.” [33:11]
• Gene drives can ensure a “killing gene” is passed almost 100% of the time, effectively dooming the species.
  • Latif Nasser: “That feels wrong. That feels like we untake. Backable.” [33:15]

Gregory Kaebnick and the Bioethics Panel

• Gregory Kaebnick (Hastings Center) convenes a symposium of environmental ethicists, ecologists, and geneticists to weigh ecological and philosophical pros and cons.
  • Kaebnick: “Here we are in the early stages of the sixth major extinction, one that we humans are causing. And I mean, in a way, this seems like, gosh, joining forces with the other side in some way.” [33:43]
• Key ethical questions:
  • Does screwworm have a valuable ecological role (pollinator, food source)? (Summary: Minimal.)
  • Is it a matter of valuing “the ingenious development [from] millennia of evolution”? [37:12]
  • Might removing screwworms have unintended ecosystem knock-ons (“hubris” argument)?
  • The panel’s reluctant consensus: screwworms are a rare candidate where full global eradication seems ethically justifiable.
    • “Most people had... said, yeah, screwworm looks like a pretty good candidate, really, that it would be okay to wipe this species off the planet forever.” [38:16]

The “Undo” Button

• If future regret arises, it may be possible to revive screwworms from preserved samples (“de-extinction”). [42:02–42:37]
  • Latif (joking about a public campaign): “We're just gonna drop these flesh-eating worms... we're just gonna rain them down over you and your home.” [42:52]

Notable Quotes & Memorable Moments

• On the logic of eradication:
  “The only way you get rid of the disease is by getting rid of the fly.” — Gregory Kaebnick [40:38]

• On the ethical discomfort:
  “I don’t want us to have to live with these, but I don’t want us to kill them forever. That feels wrong.” — Latif Nasser [33:15]

• On evolution and intrinsic value:
  “Anything that's around today has been honed by millennia of evolution... a marker of the creative natural forces that sustain life that brought us into being.” — Gregory Kaebnick [37:16]

• On the horror of human infection:
  “A patient was holding a bowl in which they were basically sneezing out and pushing out larvae from their nasal passage.” — Megan Nichols, CDC [30:22]

• On the outrageous science origins:
  “Watching insect sex all the time—not in a weird way.” — Sara Khari [12:16]

• Golden Goose Award:
  “If you ever meet someone who doesn’t believe that the government should fund basic science, just one of these [stories]—we’ll link them all in the Episode Description.” — Latif Nasser [44:18]

Timestamps for Key Segments

| Timestamp | Segment | | ----------- | ------------------------------------------------------------ | | 02:30–04:44 | Introduction and Florida deer outbreak | | 05:15–12:36 | Origins: Knipling’s life, theory, and first experiments | | 13:37–16:02 | First mass production, field success on Curacao | | 16:37–20:27 | U.S. eradication campaign and multilateral expansion | | 24:27–26:34 | 2023–present: Screwworm resurgence and government response | | 28:11–30:22 | Broader impact: wild animals, human cases, CDC perspective | | 31:08–34:11 | The treadmill: Are we stuck in perpetual eradication cycles? | | 34:11–38:16 | Ethics panel: Should we eradicate a species forever? | | 40:38–41:11 | The limits of alternatives: no medicine, only eradication | | 42:02–42:37 | The “undo button” and de-extinction | | 43:20–44:47 | Golden Goose Award and the value of basic science |

Episode Tone

The hosts strike a tone that is at once deeply curious, slightly irreverent, and ethically inquisitive—moving deftly between wonder at scientific genius, horror (and occasional humor) at the parasite’s gruesomeness, and humility regarding human intervention in nature. The debates are lively, patient, and nuanced, ultimately leaving listeners with no easy answers—and an enduring respect for both human ingenuity and the unpredictable complexity of life.

Resources Mentioned

• For further information: screwworm.gov [45:15]
• Sam Kean’s podcast "The Disappearing Spoon" (episode on screwworms)
• Sarah Zhang’s article in The Atlantic (linked in episode description)
• Radiolab’s gene drive episode: “CRISPR Update”
• Golden Goose Award: examples of basic, “silly-sounding” science with transformative impact

Summary Produced by Radiolab Podcast Summarizer, 2026.