American Oceans

The Many Ways Horseshoe Crab Blood Will Amaze You

Horseshoe crabs are unique sea creatures that have been around for millions of years. They are known for their horseshoe-like appearance and unique blood

horseshoe crab blood collected by medical field experts
Photo Credit: Jacqui Frank and Abby Tang from Business Insider

Though the blood of sea animals may not be something that is typically on your mind, these small arthropods have a unique ability flowing through their veins. 

Horseshoe crab blood has an immense impact on the medical field and lives around the world.

Believe it or not, their blood has even played a part in the COVID-19 vaccination efforts. To learn more about this miracle blood, read on!

What’s Special About Horseshoe Crab Blood?

So, what makes horseshoe crab blood stand out? For starters, the blood of these animals is actually light blue in color!

horseshoe crab blood special copper color

But why do horseshoe crabs have blue blood? The reason for this interesting hue is the level of copper in this animal’s blood.

Copper is carried in the hemocyanin, a protein which is used to transport oxygen. When the copper in their blood is exposed to oxygen, the result is an unusual color.

In addition to the color of the blood of horseshoe crabs, it is also special due to the animal’s prehistoric traits. 

horseshoe crab caught to collect blood amebocytes

As the sea creature has been around for so many years, their blood still contains a type of prehistoric blood cell, amebocytes.

Amebocytes in horseshoe crabs make an extract known as limulus amebocyte lysate (LAL), which is the real star of the show.

LAL has a very powerful ability to clot, however, the clotting only occurs when it comes in contact with bacterial toxins.

In other words, horseshoe crab blood can detect the presence of toxins. As a result, the blood is used to ensure medical equipment and other tools are in fact sterile.

For example, horseshoe crab blood is used to check the safety of pharmaceuticals, vaccines, prosthetics, and other tools used in the medical field.

Why is Horseshoe Crab Blood Important to Humans and the Medical Industry?

As mentioned above, horseshoe crab blood can ensure medical tools are sterilized and safe to use on the human body. 

Due to the fact that the use of this sea creature’s blood has been around half a century, it has been a part in the development of many vaccines like measles. 

Horseshoe crab blood even helps to keep common medical devices like IVs and implants safe. 

However, horseshoe crab blood has stepped up to the plate yet again. The blood has been used to help create the COVID-19 vaccines available in 2021. 

COVID-19 and Horseshoe Crab Blood

It is especially important to check the sterility of vaccines as they are injected into the bloodstream and could have immediate adverse effects if containing any toxins. 

horseshoe crab blood used to sterile covid-19 vaccine

Horseshoe crab blood is used every year to meet this requirement, although, with the immediate need for such a large sum of vaccines to combat the new coronavirus, there is a much higher demand for the liquid. 

In other words, horseshoe crabs are essential to guaranteeing millions of lives are saved through vaccination.

Because of this one-of-a-kind ability, the blood of these animals currently worth about $60,000 a gallon. That’s quite a hefty cost!

How is Horseshoe Crab Blood Harvested?

So, how do we get the blood from horseshoe crabs? First, they must be caught. In regard to the COVID-19 vaccine, companies are using horseshoe crabs mainly from the Maryland Coast. 

horseshoe crab harvested from Maryland coast for blood

Horseshoe crabs are typically caught during their breeding season, which is usually from May to June. 

As horseshoe crabs head to the shore to breed, they are out in the open and much more vulnerable to dangers.

Due to this, the animals are usually captured at this time, as it is much easier to do so. Once caught, a needle is inserted into the heart of these animals and they are drained of about 30% of their blood.

The blood is then separated into two substances: plasma and blood cells. From here, the LAL is extracted and freeze dried into a powder that can be used to detect bacterial toxins.

Downsides to the Use of Horseshoe Crab Blood. Though the blood of horseshoe crabs may sound like nothing short of a miracle, it’s important to address the adverse effects its use can have. 

Horseshoe crabs are not intended to be killed when they are used for their blood, however, this does not mean it doesn’t occur.

After being drained of nearly a third of their blood, the animals are supposed to be released back into the ocean. 

When this does occur, the sea creatures are not necessarily able to survive. Due to the large amount of blood loss, horseshoe crab bleeding has a mortality rate from 3-15% to 10-30%

On the other hand, some companies actually end up selling horseshoe crabs after bleeding them.

These animals can be used as bait, and surprisingly, as many as one million horseshoe crabs are captured to be used as bait in the fishing industry each year. 

For those that do survive, the bleeding process can inhibit day to day abilities of the horseshoe crab.

This is not only due to the blood loss but also to the issues presented in the transportation process of horseshoe crab bleeding. 

horseshoe crab harvested for transportation to collect blood

Specifically, the animals are typically transported on boats in very warm temperatures. Additionally, they can be kept out in the open for long periods of time and may not be able to breathe as a result of the lack of water. 

Changes in horseshoe crabs post-blood loss include a decrease in activity and hemocyanin levels. Which can indicate a higher risk of death in some cases.

The bleeding process has also shown that female horseshoe crabs may have a weakened ability or lost ability to reproduce. 

Additionally, as they are usually bled during breeding season, there are fewer horseshoe crabs to reproduce.

Further, some of these animals that are in the ocean at this time may not even travel to the shore to breed due to lessened activity.

This of course has led to a significant decrease in their population. The number of horseshoe crabs caught each year puts thousands at risk.

Specifically, as many as 550,000 horseshoe crabs are caught to be bled every year. However, this number has likely increased greatly in the past year due to the blood’s use in the coronavirus pandemic.

To put that in perspective, 10-30% of 550,000 is 55,000-165,000. In other words, this is the number of horseshoe crabs that may die from the bleeding process each year. 

The problem is, if the horseshoe crab population continues to decline, their species may be in trouble.

Without these sea creatures, the lives of many other animals in their ecosystem would be affected. Not to mention, without horseshoe crabs the medical industry could face some challenges. 

What Can We Do to Protect the Horseshoe Crab Population?

If the horseshoe crab blood industry continues to exist, there are some changes that can be made to decrease the fatality levels associated with the process.

As mentioned above, many dangers of the bleeding process actually occur during transportation.

To avoid this, some changes that could be made include releasing any horseshoe crabs that appear unhealthy before transporting them.

This would be beneficial as the animals that are already unhealthy have an increased risk of dying from the blood loss. 

Additionally, some have suggested capturing the animals at night. This would prevent the sea creatures from being in such high temperatures for so long. 

Similarly, if possible, it could be beneficial to make transportation a more efficient process by cutting down travel time.

In line with this is the idea to keep horseshoe crabs wet. This will allow them to breathe while being transported. 

Lastly, researchers have looked into some kind of supplement to help horseshoe crabs recover from the bleeding process. 

However, there is an alternative to using the horseshoe crab population in the medical industry. What is it? And why aren’t we using this alternative?

To answer this question, let’s learn a little bit of history about the use of horseshoe crab blood. 

The use of LAL in horseshoe crab blood was first discovered by Frederik Bang. In an attempt to study the immune system of the sea creature, Bang injected bacteria into horseshoe crabs and noticed the clotting reaction. 

Further, when Bang boiled the bacteria, the clotting still occurred. This indicated that the presence of toxins could be identified even if they are presumed to be gone, making this blood ideal for testing medical devices. 

Bang and his colleague, Jack Levin, eventually found an efficient way to separate LAL from the other components of the blood. The LAL test was approved by the FDA 1977.  

Flash forward half a decade and we come across Jeak Ling Ding. Ding wanted to make sure horseshoe crabs were no longer necessary for the medical industry. 

In order to do this, Ding started to look for the gene in horseshoe crab DNA that makes LAL so effective.

Specifically, she was looking for the gene that makes limulus clotting factor C or rFC. rFC is the individual component that is responsible for the clotting abilities of horseshoe crab blood.

After many years of research, Ding had created a way to produce a synthetic version of rFC. This process was patented in 2003 but unfortunately has not been widely used by the medical industry. 

There are a few reasons the industry has been hesitant to use this synthetic alternative. First, the new test has not been approved by regulators such as the FDA.

This could cause issues in regard to litigation and other risk factors regulation may help companies avoid. 

Additionally, there is only one manufacturer for the alternative. If Ding’s test is widely accepted, it could be difficult for the manufacturer to keep up with demand. 

Lastly, the horseshoe crab blood industry has quite a bit of money tied up in it. If this industry dies, many companies will lose money.

As you can imagine, they’re not very keen on the idea. Despite these concerns, the U.S. Senate actually encouraged the FDA to approve alternatives to horseshoe crab bleeding in 2019. 

However, the synthetic version has yet to be approved by the U.S. as equally effective as the horseshoe crab blood, but it shows promise that a different tactic may be used soon.


Overall, it is interesting to see the multiple ways in which horseshoe crabs affect our everyday lives. Even more so, many individuals probably hadn’t even heard of these animals until recently. 

There is no doubt about the fact that horseshoe crabs are invaluable to the ocean and land with their unique capabilities. 

Though these sea creatures have had an immense impact on the health and well-being of many humans, it’s arguable that we must make an effort to give back to these animals. 

The horseshoe crab bleeding process has a detrimental effect on the populations of these amazing animals.

Through more research and approvals, it is possible to completely eliminate the use of horseshoe crab blood in the medical industry. 

While it can be hard to imagine the next steps in the process toward using a more humane approach, research shows there’s a light at the end of the tunnel. So the next time you think about horseshoe crabs, be thankful!


  • If nothing has happened to protect this animal by now it will be extinct. It’s reprehensible but the Almighty dollar reigns in America. Feathers for hats and skins for rich people destroyed many species already. Sad but a fact that this Remarkable animal is used for Bait? Truly criminal.

  • My suggestion is to start a horse shue crab farm at Monterey Bay aquarium and only bleed the mail crabs so the females can lay the eggs.

  • I work in the pharmaceutical microbiology industry and we use LAL to detect endotoxin in medications and raw materials. Thankfully, there are some new methods that require a fraction of the volume of LAL required for testing. I know there is a synthetic version of LAL in the works, and I hope it’s available for use soon! These crabs have been little miracles for long enough and deserve to be left alone