Horseshoe crabs are not much to look at. But beneath their unassuming catcher’s-mitt shell, they harbor a half-billion-year-old secret: a superpower that helped them outlive the dinosaurs and survive all the Earth’s mass extinctions. And what is that secret superpower? Their blood. Their baby blue blood. And it’s so miraculous that for decades, it hasn’t just been saving their butts, it’s been saving ours too. But that all might be about to change. Follow us as we follow these ancient critters - from a raunchy beach orgy to a marine blood drive to the most secluded waterslide - and learn a thing or two from them about how much we depend on nature and how much it depends on us. BONUS: If you want to know more about how miraculous horseshoe crabs are, here's a bunch of our favorite reads: 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 or check out Glenn Gauvry's horseshoe crab research database This episode was reported by Latif Nasser with help from Damiano Marchetti and Lulu Miller, and was produced by Annie McEwen and Matt Kielty with help from Liza Yeager. Special thanks to Arlene Shaner at the NY Academy of Medicine, Tim Wisniewski at the Alan Mason Chesney Medical Archives at Johns Hopkins University, Jennifer Walton at the library of the Marine Biological Lab of the Woods Hole Oceanographic Institution, and Glenn Gauvry at the Ecological Research and Development Group. Support Radiolab today at Radiolab.org/donate.