Short Wave

Parasites Have Haunted Us For Millions Of Years

October 24, 2025

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  • Parasites have an ancient history, with fossil evidence dating back over 500 million years, predating the dinosaurs. 
  • The mysterious fossil known as the “Riddler” was identified as an ancient parasitic worm (a spionid) that built tubes on brachiopods, demonstrating the long-term resilience of parasitic lifestyles. 
  • The discovery of the oldest-ever leech fossil, *Macromyzon*, suggests that early leeches likely preyed on invertebrates or were parasites of invertebrates, rather than feeding on vertebrate blood as was previously hypothesized. 

Segments

Introduction and Parasite Definition
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(00:00:18)
  • Key Takeaway: Parasitism is a specific form of symbiosis where one organism gains nutrients at the expense of a host, requiring specific adaptations.
  • Summary: Regina Barber opens the Short Wave episode, “Parasites Have Haunted Us For Millions Of Years,” by asking for the definition of a parasite. Parasitism is defined as a type of symbiosis where one organism lives on or inside a host, gaining nutrients at the host’s expense through specialized adaptations. This relationship is distinct from other forms of long-term species association.
Ancient Parasite Fossils
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(00:01:08)
  • Key Takeaway: Fossils showing evidence of parasites are over 515 million years old, found on brachiopods, predating dinosaurs.
  • Summary: The discussion reveals that parasites have existed for at least 515 million years, evidenced by worm-like animals building tubes on shelled creatures called brachiopods to steal food. Tracing these origins is difficult because parasites are usually soft-bodied and rarely preserve well in rock. An example of a well-preserved fossil parasite includes nematodes emerging from plant hoppers trapped in amber.
Solving the Riddler Mystery
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(00:02:16)
  • Key Takeaway: The mysterious fossil dubbed the “Riddler” was identified as an ancient parasitic worm, a spionid, based on its trace structure matching modern relatives.
  • Summary: Paleontologist Karma Nanglu describes the years-long investigation into the fossil marked with a question mark, nicknamed the “Riddler.” By comparing the trace structure to modern worms, the team identified it as belonging to an ancient spionid worm. This identification reveals the worm’s behavior: boring into a shell, building a tube home, and feeding on water currents, behavior well-characterized in modern relatives.
Leech Fossil Discovery
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(00:09:07)
  • Key Takeaway: The first fossil leech, Macromyzon, was discovered in Wisconsin fossils, suggesting early leeches were invertebrate parasites or predators, not vertebrate feeders.
  • Summary: Danielle de Carle explains that modern leeches exhibit diverse feeding habits, including swallowing prey or sucking fluids from invertebrates like crabs. The newly identified fossil leech, found without large vertebrates nearby, suggests its ancestors either preyed on animals whole or parasitized invertebrates like trilobites. This discovery pushes the leech lineage back 200 million years older than previously thought and challenges the hypothesis that the first leeches fed on vertebrate blood.
Future of Fossil Discovery
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(00:14:04)
  • Key Takeaway: Significant future paleontological breakthroughs are expected from re-examining existing, unstudied fossil collections using new technologies like CT scanning.
  • Summary: Both experts agree that vast potential for discovery lies within existing fossil collections that have not been fully analyzed or published. New technologies, such as CT scanning, allow researchers to scrutinize known fossils for traces of soft tissue or previously unseen organisms, like finding new evidence inside existing specimens. Exceptional preservation sites, like the Waukesha site in Wisconsin, offer rare, complete snapshots of ancient life.