TED-ED: Why do we harvest horseshoe crab blood? - Elizabeth Cox

During the warmer months, especially at night during the full moon, horseshoe crabs emerge from the sea to spawn. Waiting for them are teams of lab workers, who capture the horseshoe crabs by the hundreds of thousands, take them to labs, harvest their cerulean blood, then return them to the sea. Why? Elizabeth Cox illuminates the incredible properties of horseshoe crab blood.