Horseshoe Crabs, otherwise known as living fossils are some of the oldest animals in the world. Their ancestors date back to 445 million years ago, which is 200 million years BEFORE dinosaurs. Because of their name, most people think they are crustaceans but they are actually more closely related to arachnids. There are four different species of horseshoe crabs including Carcinoscorpius rotundicaud, Tachypleus gigas, Tachypleus tridentatus, and Limulus polyphemus, which is the only species found in North America.

Organism Structure

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Horseshoe crab” by Wikimedia Commons under CC by 2.0



Photos taken during Invertebrate Zoology class.

Over the millions of years, the body structure of the horseshoe crab hasn’t changed drastically. Their body is surrounded by a hard carapace, which is used for protection. There are two compound lateral eyes that consist of one thousand ommatidia. Ommatidia are clusters of photoreceptor cells surrounded by support and pigment cells. Along with their two lateral eyes, they also have two median eyes that can see visible and UV light, one endoparietal eye, and two more rudimentary lateral eyes on the top of their body. Horseshoes crabs have five pairs of legs, and their mouth is located in the center of them. They have no endoskeleton, and have book gills which function as an exchange of respiratory gases.

Horseshoe Crabs importance in the Medical Industry

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Bleeding Crabs” by under CC by 2.0

Human blood is iron based, and a horseshoe crab’s blood is copper based which give it its blue color. When bacteria or endotoxins try to enter their blood stream, the blood will “gel” and create a barrier against the bacteria. A horseshoe crab’s blood is made up of only amebocytes ,which are mobile cells that act as a defense like white blood cells do in vertebrates.

The biomedical industry has conducted a way to extract this compound from their hemolymph and use it for medical treatment. The preparation is called Limulus Amebocyte Lysate (LAL). The goal of this treatment is to detect endotoxins that are associated with gram negative bacteria. This bacteria activates a pyrogenic response when it comes in contact with human blood. Because of the detection function, it is used in biomedical companies to test vaccines, IV drugs and implants for any signs of bacteria contamination.

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“Vaccine” by Wikimedia Commons under CC by 2.0

The Controversy

During the preparation of LAL, the horse shoe crabs are not killed. About one third of their blood is extracted. They are then released back into their habitat where they came from. Researchers estimate that it takes thirty days for the horseshoe crab to replace their missing blood. There are about 500,000 animals collected annually for medical testing. The mortality rate is about 10%, which scientists argue “could be a lot more”. Some argue that this preparation is in dire need to make sure medical equipment is sterile, while others argue it is unethical and animal cruelty. Bleeding of the females may prevent them from being able to spawn and can decrease the amount of eggs laid. Some biomedical companies get accused of not putting them back to the ocean but instead selling them as fishing bait, which is the horseshoe crabs other main “use”. As a result of this controversy, the legislation has put a limit on how many horseshoe crabs can be harvested, and the horseshoe population is now increasing. Personally, I understand the  health benefits of using horseshoe crab blood to test for sterile medical treatment, but I don’t understand why we are so advanced in technology but cannot come up with a different way to test that does not use animals.






8 thoughts on “Horseshoe Crabs In the Medical Industry

  1. Wow! That picture of bleeding horseshoe crabs is really creepy! You raise some great questions here. At what point do benefits to humans outweigh negative effects on animals like this to justify the practice? How much does their ability to sense pain weigh into the answer? Ecological effects on their populations seem to also be pretty big. Would love to know what other students in the class think.

    Liked by 1 person

    1. Love the article! Ive heard about this process of extracting horseshoe crab blood for medical purposes but I never understood the exact reason why. I can see the fine line in which people may feel the 10% death rate is unjust and I agree with you when you mention there should be better ways to perform this research. With the advancements we as humans have made in the scientific and medical fields, you would think these animals wouldn’t have to be harmed in any way. With these crustaceans being so old and almost untouched evolutionarily for so long, I believe there is no way we can risk affecting the population of such a scientifically interesting organism which roamed the earth with the dinosaurs.

      Liked by 1 person

      1. I completely agree with you Devon. They have been around for so long and because of their use for the medical field, populations were declining. This is a perfect example of what human impact could have on an organism’s population.

        Liked by 1 person

    2. I think that a synthetic compound could be made with today’s technology that carries out the same job as the horse shoe crabs blood. For my senior thesis it also uses animals for medical equipment. I am writing about the Edwards SAPIEN transcatheter heart valve, which is made from cow skin. This has been the most durable material they have found yet. I think this medical equipment made from animals to benefit humans can be justified, but bleeding animals just to check if something is sterile? This could just be my bias opinion, but I believe the medical industry is just not trying hard enough to find a better solution. Regarding the question of their ability to sense pain, despite what scientific thinking suggests about inverts not possessing a Neocortex (where pain registers), researchers do believe they can feel pain. I don’t think it weighs into the industry at all and I don’t think it is a consideration for the companies that are making money off of it. I made a poll on twitter to see what other members of the class think!

      Liked by 1 person

  2. This is a great post! I have never heard of horseshoe crab blood being used for medicine. You mentioned the controversy over it but do you know if their population has decreased since they have started being used for medicine?


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