Be Kind to Horseshoe Crabs


You have seen them on the beach and, chances are, if you have frequented beaches further north, you have likely seen lots of them. Horseshoe Crabs are one of the oldest creatures on the planet, often referred to as “living fossils.” Older than dinosaurs, they have been around for some 445 million years and are nearly identical to their original ancestors.

But their name is a misnomer because they are not crustaceans. Horseshoe Crabs are arthropods, more closely related to spiders and other arachnids, and they are built for survival. They look like army tanks with a large hard carapace, ten legs, and a spikey tail that can appear menacing. Of course, they are harmless and that tail (telson) serves a simple purpose which is to help flip the animal back upright when it gets turned over by a wave.


While horseshoe crabs are not really crabs, most definitely not edible, and seem to go about their business of survival in a benign manner, these animals are key to human health. In fact, if you have ever been vaccinated or received any kind of intravenous drugs, you probably owe your life to them. That is because they are the only animal on earth with a blood-clotting agent known as Limulus Amebocyte Lysate, or LAL, which clots in the presence of certain groups of bacteria. Their blood is blue in color because of the presence of copper in hemocyanin, a protein that carries oxygen.



Horseshoe crab blood is used to test sterility of medical equipment and prosthetics including implants, heart stents, pacemakers, and all injectable and vaccines. The FDA requires the use of LAL to test such drugs to detect the presence of harmful bacteria (contamination) and has been doing so for over 30 years. The good news is that harvesting horseshoe crab blood is not particularly dangerous and most of the animals are released back to the ocean. But there is skepticism about the mortality rate which can be as high as thirty percent depending upon transport conditions, stress, and the amount of blood that is harvested. Pressure from some animal rights and environmental groups prompted several pharmaceutical companies to manufacture a synthetic alternative but to date, The United States Pharmacopeia, published annually by the United States Pharmacopeial Convention does not consider the synthetics to hold up to the gold standard of LAL from horseshoe crab blood.


Approximately 500 thousand horseshoe crabs are collected annually for blood harvesting. Fortunately, amid the race to develop a vaccine for COVID-19, the amount of LAL necessary for safety testing is minimal and industry experts say that it would take only a day of production to manufacture enough to assure the purity of even an estimated five billion doses. The LAL test was first developed by Massachusetts Biological Laboratory and subsequently licensed and manufactured beginning in 1974 by Associates of Cape Cod. The test replaced the horrifying practice of using rabbits for the same purpose.


When you encounter one of these fascinating creatures on the beach remember all they have done for humanity (and rabbits) and proceed with care. Horseshoe crabs breed at night during high tides, under new and full moons. They nest on the beach so if you see them on the shore, leave them alone. If you encounter one that has been turned on its back, gently turn it back over. Never handle or pick up a horseshoe crab by its tail as this will injure the animal.

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