Radiolab – "Parasites" (September 7, 2009, WNYC Studios)

Episode Overview

In this enthralling episode, Radiolab dives headlong into the hidden world of parasites—those often-invisible organisms that live within and upon us, sometimes shaping our biology, our behaviors, and even the fate of civilizations. Hosts Jad Abumrad and Robert Krulwich, alongside contributor Lulu Miller, explore parasites from all angles: as villains, clever survivors, evolutionary partners, unwitting healers, and even as subtle puppet-masters influencing the minds and actions of animals and humans alike. With dynamic storytelling and signature Radiolab sound design, the episode moves skillfully from cinematic pop culture to historical public health, current immunology, and philosophical questions about free will.

Key Discussion Points & Insights

1. Starting with Horror: The Cinematic Roots of Parasite Fear

• Opening (00:18–04:06)

  • The episode frames the universal fear of parasites with the infamous "chestburster" scene from the film Alien, using its visceral shock to prime listeners for the uncomfortable reality: real parasites aren’t far off from sci-fi monsters.

  • Quote:
    “It's not that the little creature is disgusting, which it is. It's that it was there all along.”
    – Jad Abumrad (03:24)

  • Insight: The horror is not the grossness, but the idea of something hidden inside us, a motif carried through the episode.

2. What is a Parasite? Challenging the Notion of Degeneracy

• Defining Parasites (04:06–07:09)
  • Science writer Carl Zimmer, introduced as a lifelong “Defender of Parasites,” joins the hosts to debunk the assumption that parasites are simple degenerates or "cheaters."
  • Carl argues for their evolutionary ingenuity and blurs the lines between independence and dependence among organisms.
  • Quote:
    “People have been dismissing parasites for a long time, calling them degenerates. Now, I would argue that parasites are not degenerate. ... They have gained the ability to live inside three, four, five, six different species.”
    – Carl Zimmer (05:53)

3. The Parasite Lightning Round: Nature’s Most Bizarre Manipulators

A. Parasitic Wasps – The Wasp and the Cockroach Puppet (08:03–12:37)

• The wasp Ampulex compressa locates a cockroach, stings it to paralyze, then performs precision brain surgery with a second sting, turning the cockroach into a zombie it can lead home.
• The wasp’s larva is laid onto the cockroach and slowly consumes it from the inside, keeping it alive as long as possible.
• Quote:
  “It just stands there like, ‘I’m awake.’ But it can’t run away, can’t move. It has essentially lost its will.”
  – Carl Zimmer (09:36)
• Darwin himself supposedly said God shouldn’t be blamed for having created such wasps (11:51).
• The segment invites the listener to judge whether such behavior represents "evil" or "elegance."

B. Parasitic Nematodes – The Ant with the Cherry Red Butt (12:54–14:22)

• Zimmer describes a nematode parasite that turns an ant’s abdomen bright red and alters its behavior, causing birds to eat the ant, thereby allowing the parasite to reproduce inside the bird.
• Quote:
  “That red cherry is actually parasites inside of the ant, making it look like a red cherry.”
  – Carl Zimmer (13:09) “It's amazing.”
  – Carl Zimmer (14:22)

C. Blood Flukes – Eternal Monogamy in the Veins (14:38–17:52)

• The blood fluke’s life cycle advances from snails to human veins, where male and female flukes "spoon"—mate and remain attached for decades, sometimes as long as 40 years.
• Quote:
  “I do love the thought that parasites are among the most monogamous animals on the planet. It's heaven. I mean, you’re going to spend the rest of your life together.”
  – Carl Zimmer (17:37)

4. Parasites as World-Changers: The Hookworm and the American South (21:17–29:41)

• The Hygiene Revolution
  • Parasitologist Dixon Despommier recounts how Rockefeller's commission discovered that widespread anemia (“laziness disease”) in the rural South was caused by hookworms, contracted mostly by barefoot farmers defecating in the open.
  • Realization: Hookworms could crawl four feet from feces; solution: bury waste six feet deep—the birth of the outhouse. This sanitation revolution drastically reduced hookworm, transformed public health, and arguably contributed to the economic revitalization of the South.
  • Quote:
    “The outhouse was invented by exploring the life cycle of hookworm ... and, in fact, Rockefeller got his wish. The South did rise again.”
    – Dixon Despommier (28:04)

5. Parasites as Saviors? Hookworms and the Hygiene Hypothesis (30:25–44:17)

Jasper Lawrence’s Story & the Theory of Beneficial Infection

• Jasper Lawrence, a lifelong allergy and asthma sufferer, discovers research suggesting hookworm infection dramatically reduces allergies and autoimmune symptoms (the “hygiene hypothesis”). Since he can’t buy hookworms, he travels to Cameroon, finds latrines, and deliberately infects himself.

• After self-infection, Jasper’s allergies and asthma vanish.

• Quote:
  “The day I realized that I no longer had allergies ... I just started screaming in the car. I was so, so happy. And I haven't had an asthma attack since ... The vast majority of the benefit that I've experienced just come from hookworm.”
  – Jasper Lawrence (35:57)

• Jasper starts selling hookworm doses via mail—though the practice is not FDA-approved and remains controversial, with serious safety and ethical concerns.

• Immunologist David Pritchard self-infects with 50 hookworms as part of a safety trial, reporting “pain in the gut” but surviving. He stresses that evidence for therapeutic benefit still requires further study.

• The hygiene hypothesis holds that lack of evolutionary “old friends” like parasites may lead to a spike in auto-immune disorders in sanitized societies.

• Quote:
  “We function like rainforests, we're ecosystems, and we've entirely eliminated a class of organism that co-evolved with us ...”
  – Jasper Lawrence (39:20)

6. Parasites as Puppet Masters: Toxoplasma Gondii and Mind Control (46:06–55:51)

The Toxoplasma Paradox

• Producer Ellen Horn recounts her scare with potential toxoplasma infection during pregnancy, which segues into a discussion with neuroscientist Robert Sapolsky.

• Toxoplasma gondii can only reproduce in cats; it infects rodents and rewires their brains so they are attracted to (instead of afraid of) cat smells, increasing the chance they are eaten by cats.

• Quote:
  “Toxo knows how to make cat urine smell sexy—to rodents."
  – Robert Sapolsky (50:45)

• There is speculative evidence that Toxo might affect human behavior, with some studies showing a correlation with higher rates of schizophrenia and increased risk-taking (e.g., car crashes).

• Epidemiologist Dr. Fuller Torrey points out schizophrenia’s rise in the 19th century paralleled the "cat craze" in urban Europe/America, leading some to hypothesize an indirect link.

• Philosophical Note:
  “Even lurking in that 1/2 of 1% are some serious implications for thinking about free will. We haven't a clue the biology lurking in the background that makes free will seem a little bit suspect.”
  – Robert Sapolsky (55:22)

• Ellen’s own test turns up positive for past toxoplasma infection, but her pregnancy continues healthy and happy.

Notable Quotes & Memorable Moments (with Timestamps)

• “It's not that the little creature is disgusting, which it is. It's that it was there all along.”
  – Jad Abumrad ([03:24])
• “I think I'm a defender of all neglected and put upon species out there.”
  – Carl Zimmer ([06:11])
• “It just stands there ... it's become a zombie, basically. ... It's amazing.”
  – Carl Zimmer ([09:36] & [14:22])
• “The outhouse was invented by exploring the life cycle of hookworm ... and, in fact, Rockefeller got his wish. The South did rise again.”
  – Dixon Despommier ([28:04])
• “The day I realized that I no longer had allergies ... I just started screaming in the car. I was so, so happy.”
  – Jasper Lawrence ([35:57])
• “Toxo knows how to make cat urine smell sexy—to rodents.”
  – Robert Sapolsky ([50:45])
• “Even lurking in that 1/2 of 1% are some serious implications for thinking about free will.”
  – Robert Sapolsky ([55:22])

Segment Timestamps

• [00:18] – Opening with Alien scene, fear of parasites
• [04:06] – Carl Zimmer and the philosophy of parasites
• [08:03] – Lightning round: parasitic wasp/roach story
• [12:54] – Lightning round: nematode/ant story
• [14:38] – Lightning round: blood fluke love story
• [21:17] – History: Hookworm, public health, outhouse
• [30:25] – Jasper Lawrence and therapeutic hookworm hypothesis
• [46:06] – Parasites and behavior: can parasites control us?
• [48:00] – Toxoplasma gondii, cats, rats, humans, mind control
• [54:08] – Toxo, schizophrenia, the “cat craze,” free will
• [55:22] – Free will and parasite influence
• [56:02] – Ellen Horn’s test, conclusion

Tone and Storytelling Style

The hosts approach parasites with a blend of awe, disgust, humor, and scientific curiosity, using vivid analogy, dramatizations, and sound-rich scenes. Carl Zimmer’s championing of parasites as complex, remarkable creatures is set against Robert Krulwich’s skeptical humor and Jad Abumrad’s wide-eyed wonder. Personal stories, historical vignettes, and imaginative leaps invite listeners to see parasites not merely as pests, but as major evolutionary players and surprising healers—as well as sinister manipulators. The episode closes with a sly nudge toward philosophical humility: if even a microbe can alter who we are, how much of our selfhood and free will is truly ours?

Additional Resources

• Pictures & Info: Find more about parasitic wasps, "cherry-butt" ants, blood flukes, and hookworm at radiolab.org.
• Key Books:
  • Carl Zimmer, Parasite Rex
  • Dixon Despommier, Parasitic Diseases
• Further Research: Studies on the hygiene hypothesis, Toxoplasma and mental health, and clinical trials on therapeutic helminths.