We’re back with an episode from the Radiolab archive. Horseshoe crabs have been around for a long time. They outlived the dinosaurs, survived all mass extinctions and witnessed the sprouting of the Earth’s first trees. The secret to their longevity? Their baby blue blood. Which has been saving both their lives and ours.

Lulu and Radiolab co-host, Latif Nasser, head to one of these bleeding facilities to learn how horseshoe crab blood became indispensable for modern medicine. And how this vampirish relationship humans have with the crabs might also be crucial to keeping them alive.

Terrestrials will be back in September 2025 with all new episodes airing every other week! SIgn up for our newsletter here and follow us on Instagram @terrestrialspodcast for updates.

If you want to learn more about how miraculous horseshoe crabs are, check out:

Alexis Madrigal, "The Blood Harvest" in The Atlantic, and Sarah Zhang's recent follow up in The Atlantic, "The Last Days of the Blue Blood Harvest"

Deborah Cramer, The Narrow Edge

Deborah Cramer, "Inside the Biomedical Revolution to Save Horseshoe Crabs" in Audubon Magazine

Richard Fortey, Horseshoe Crabs and Velvet Worms

Ian Frazier, "Blue Bloods" in The New Yorker

Lulu Miller's short story, "Me and Jane" in Catapult Magazine

Jerry Gault, "The Most Noble Fishing There Is" in Charles River's Eureka Magazine

Glenn Gauvry's horseshoe crab research database

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The Horseshoe Crab's Secret

Radiolab for Kids