A substance in the crab's blood is used for to test intravenous drugs for bacterial contamination. After bleeding, the crabs are returned alive to the ocean. The horseshoe crab is a real blue blood, an aristocrat of the sea whose numbers are dwindling. Unlike the red blood of other animals, which contains iron, horseshoe crab blood has copper in it, which stains the liquid a shimmering blue. Delaware Bay is the largest spawning center for the Atlantic horseshoe crab.
Biologists say their numbers are decreasing.
A test was developed that is now the worldwide standard for screening injectable drugs for contamination by human pathogens. The FDA made the test mandatory in the final testing of new intravenous drugs in the 1970s. The horseshoe crabs aren't killed when their blood is taken for the tests, but other factors are thinning populations of the vital arthropod. Decrease in Delaware Marine biologists say a combination of over-fishing and loss of habitat have taken their toll on the archaic creatures. The horseshoe crabs, he explains, are prized bait for catching conch and eel.