Horseshoe crabs are trapped and drained of almost two-thirds of their blood. They are tagged so they are not used again too soon. A chemical in their blood causes it to form a clot when exposed to gram-negative bacteria. This bacteria can cause death in humans if it reaches the bloodstream.
Scientists use horseshoe crab blood to test syringes and artificial joints and any equipment that comes in contact with the human bloodstream, to make sure the gram-negative bacteria is not present. Before this discovery of the properties of horseshoe crab blood in the 1970s, scientists used live rabbits to test for the bacteria. The rabbits got a fever if the bacteria was present.
If you recently got a flu shot or any other vaccine, thank a horseshoe crab that the needle and medicine were safe.
