The horseshoe crab has endured for over 450 million years. It has survived several mass extinctions including the one that killed off the dinosaurs. One reason for their incredible resiliency is their ability to fend off bacterial infection. Their blood contains cells that clot around invading bacteria, thereby protecting them from the attacking toxins. In this episode we talk with three experts about how this animal’s unique blue blood has become essential to modern medicine. We also talk about why horseshoe crab populations are dwindling, and what biotech is doing to address the shortfall.