Horseshoe crabs are not true crabs but are arthropods related to another ancient fossil animal, the trilobite. Trilobites became extinct long ago, but horseshoe crabs are still around and living in many areas of the world.
Horseshoe crabs are not attractive to look at or popular for eating. Outside of possible use as fish bait, what use do they have? For one thing, their eggs are an important food for certain migrating shorebirds called red knots. However, the most important direct use for humans is in the field of medicine. If you have ever taken a prescription, received an immunization, had a hip or knee replacement, received an organ transplant, or even had an IV, you can thank the horseshoe crab for the good that came from that medical treatment.
When bacteria enter the horseshoe crab’s body, amebocytes in its blue blood immediately clot around the bacteria, trapping it. The blood from horseshoe crabs is used to test for bacterial endotoxins in pharmaceuticals and testing for bacterial infections. If harmful bacteria are present, the blood will form a clot. Horseshoe crabs are captured by medical researchers to use their blood for testing. After bleeding, they are returned to the ocean. Like humans who give blood, the horseshoe crab’s blood supply soon returns to normal.
Even a “worthless” creature like the horseshoe crab is uniquely suited to help in human survival. We see another example of design in the world around us. The Designer knew there was a need for this animal. We are more than “lucky” to have the horseshoe crab.
© Roland Earnst