The animals are drained of some of their blood and returned to the natural environment, but lots of die from the bleeding. Its blue blood is harvested for medical researchers and used by drug and medical product makers to test for harmful impurities in vaccines, prosthetics and intravenous prescription drugs. https://horseshoecrabbloodamiracl55956.liberty-blog.com/30364308/the-5-second-trick-for-horseshoe-crab-blood-chemical