Medical uses for the Horseshoe Craba bottle of horseshoe crab blood, it is a bright blue color
Horseshow Crab Blood

The blood of the horseshoe crab provides a valuable medical product critical to maintaining the safety of many drugs and devices used in medical care. A protein in the blood called Limulus Amebocyte Lysate (LAL) is used by pharmaceutical and medical device manufacturers to test their products for the presence of endotoxins, bacterial substances that can cause fevers and even be fatal to humans.

The LAL test is one of the most important medical products
derived from a marine organism to benefit humans.

Why is the Horseshoe Crab the original "blue blood"?

A horseshoe crab's blood has a blue to blue-green color when exposed to the air. The blood is blue because it contains a copper-based respiratory pigment called hemocyanin.

Additional references.


  • Stacy Epperson
    Education Specialist
    Aquatic Resource Education Dept
    Watershed Services
    Department of Natural Resources
    580 Taylor Ave., E-2
    Annapolis, MD 21401
    Phone: 410-260-8775