Horseshoe crabs- Miracle Blood

The classification of the Horseshoe crab is as follows: Phylum Arthropoda, Class Merostomata,  Family Limulidae, Genus Limulus, Species polyphemus . An adult female Limulus will attain lengths of 24 inches.  Most first time encounters can be rather scary, because they also have a very long spiked tail. Contrary to public opinion, the tail is quite harmless and the horseshoe crab should never be picked up this way. This unique creature lives on sandy or muddy bottoms.  Because of its propensity to burrow, it prefers a softer sediment.  It frequents intertidal and sub-tidal regions, rarely going deeper than 75 feet.  The Atlantic Horseshoe crab may be found from the Gulf of Maine all the way to the Gulf of Mexico. They start of life very light in color.  When small, they are a sand color and, as they molt and grow older, they darken.  After the terminal molt, they are a deep brown color.


Most animals have red blood. Our blood is red thanks to the presence of iron (Fe) in our hemoglobin. Hemoglobin transports oxygen, and since oxygen has poor solubility in water, iron is needed to bind those oxygen molecules onto the hemoglobin.

Some animals are different and have blue-colored blood. Some examples of the blue bloods are the octopus and squid, along with the humble Horseshoe Crab.  They all have blue blood, thanks to the presence of copper as oxygen-transporting agent in their blood, and the blue-colored copper-based molecules are called hemocyanin. 

Limulus has an interesting history as well.  It was once used en masse as a fertilizer.  Tens of thousands were harvested and spread on fields to fertilize for the summer harvests.  It was a cheap source of fertilizer, since the flesh of the Limulus is inedible to humans and they are considered a nuisance species.  Most clam and oyster farmers dislike the presence of Limulus because they can disrupt their beds and, in the summertime, the beaches are clogged with thousands of crabs.  Trawlers also dislike the tons of crabs that take up valuable net space each year.  So, these animals were collected with little regard.  It was not until the 1970’s that scientists found a special use for Limulus.
Scientists have found out that the blue blood of Horseshoe Crabs does miraculous thing: when a crab gets injured and its insides are exposed to invading bacteria, a particular blood cell explodes, sending a mass of blood-clotting granules that instantly block out the invaders. Thi is invaluable for testing the sterility of pharmaceuticals, more about this later. Our blood clots too, thanks to the platelets in our blood. 

Frederick Bang first discovered the awesome quality of the Horseshoe Crab’s blood in the 1950s. He realized that the blood could serve as an alarm system to protect products (human cells, DNA) from contamination, as the blood clot as soon as there is any sign of negative bacteria.It was later recognized that the animal’s blood cells, mobile cells called amoebocytes, contain granules with a clotting factor known as coagulogen; this is released outside the cell when bacterial endotoxin is encountered. The resulting coagulation is thought to contain bacterial infections in the animal’s semi-closed circulatory system. He isolated the clotting agent and called it Limilus amoebocyte lystate (LAL), and a quart of this LAL could cost up to $15,000. A high-profit investment indeed. 
Fishermen would harvest crabs, extract their blood, sell the serum to pharmaceutical companies, and return the crabs to the wild. But not all crabs survive the ordeal–3~15% of the crabs die after being bled. As a result, the population of Horseshoe Crab in some states in the U.S has dropped significantly.It is now illegal to purposely kill Limulus in most coastal states.


The Horseshoe Crab is one of the oldest creatures to ever walked the Earth. It has outlived the dinosaurs, and has had millions of years to perfect its defense system against invincible enemies. We seek to “borrow” their blood for our own interest, so it would be a shame if we fail keep the species alive in the end.It is always fascinating to observe a true living fossil, but these creatures are best left in nature.  If one is fortunate enough to see one at the beach, please keep a few things in mind.  They are 100% harmless.  Never pick them up by the tail, but grasp firmly onto the carapace and hold them.  They will thrash about , ‘close up,” and try for form a ball, but eventually they will relax,  and one can then observe the book gills, chelicerae – and even tell if it’s a boy or girl.  In males, the first pair of appendages, the chelicarae, have a thickened claw, much like boxing gloves.  The females do not have this.  And if, by chance, on a spring time full moon night at an East coast beach, you happen to be walking along the sand, keep your eyes open for one of the most spectacular events you will ever see.