Horseshoe Crab Blood: How It Can Save Your Life

Horseshoe Crab Blood: How It Can Save Your Life

We just got our first COVID-19 vaccine. Which is a little scary since the vaccine is brand new.

But we take comfort the vaccine is free of bacteria since it is tested with a substance called LAL. But our comfort quickly vanishes when we learn LAL is made from the blood of horseshoe crabs. Whoa. Horseshoe crab blood! How can that be?

First, let’s start off with what is a horseshoe crab? And why are they described as living fossils?

horseshoe crab blood

Horseshoe crabs have been around for 450 million years.

horseshoe crab blood

Horseshoe crabs are more like spiders than crabs. Illustration: Peppermint Narwhal.

First, What Is A Horseshoe Crab?

Well, they are a prehistoric-looking animal living in the shallow waters along the coast. We have one species in North America, the Atlantic horseshoe crab.

Older than dinosaurs, they have been around for 450 million years. How cool! And they are not really crabs but closer to spiders (learn about spiders in our Underdog section on Spiders).and scorpions.

But like so many misunderstood animals, their populations are decreasing due to overharvesting, loss of habitat and use by the medical industry. OK, tell me more.

horseshoe crab blood

A bottle of horseshoe crab blood.

Horseshoe Crab Blood

But back to why they help keep us safe. Did you know we rely on horseshoe crabs to make sure our blood supply is free of bacteria? Really?


When exposed to toxins, the crabs use their blood, which is blue from the copper in it, to isolate the toxin and enclose it with a gel.  This gel keeps them from getting sick. When the crab’s blue blood is exposed to human blood, it reveals any bacteria that might otherwise go undetected.


As a result, all intravenous drugs, shots and vaccines in the US are required by the FDA to be tested with horseshoe crab blood to detect any foreign bacteria. Wow! That includes your flu shot, your dog’s rabies shot and your Covid vaccine.


Also, your medical implant has been checked for contamination using the horseshoe crab’s blood. Think knee or hip replacement and even your contact lens.

Is There An Alternative to Horseshoe Crab Blood?

The short answer is absolutely, but not in the United States. A number of European countries, Japan & China all use a synthetic equivalent to LAL. So why don’t we?

Well, it is complicated. For an in depth study on the subject, check out a great article published in Feb 2021:  Vaccine testing is changing. Why is this 13B lab still bleeding horseshoe crabs? (The link is at the bottom under How Can We Help?)

The bottom line: we should be pushing the FDA to approve synthetic LAL.  It will help save our horseshoe crabs and still provide a safe way to test our vaccines and medical equipment.


horseshoe crab blood

Looking inside a horseshoe crab, their blood is actually blue.

horseshoe crab blood

Thousands of horseshoe crabs are captured in order to get some of their blue blood

Horseshoe Crab Populations Are Declining

So how is their blood harvested and does it hurt the horseshoe crab? The crabs are caught, transported to a lab and hooked up to a machine that pierces their shell and drains 30% of their blood. Yikes, we sound like vampires! The crabs are then returned to the ocean where some (estimates range from 10-30%) die or stop reproducing.

The crabs are also harvested as bait for fishing further reducing their populations. Horseshoe crabs are now classified as Vulnerable by the International Union for Conservation of Nature (IUCN), which means they are likely to become endangered if conditions do not improve.

How Can We Help?

horseshoe crab blood

If you see a horseshoe crab upside down, please turn it over so it can live

They do so much for us, so what can we do for them?  To begin with, if you see one upside down and alive, gently turn it over so it can live. They get tumbled about in the waves and have no way of righting themselves if flipped.

Second, you can learn all you can about these incredible creatures and truly appreciate all they do. Become an advocate for research to find alternative methods of testing for toxins. Or at a minimum, support groups that are finding ways to reduce the mortality rate and stress factors while harvesting their blood.

We owe our lives to horseshoe crabs. Let’s protect them because it is the right thing to do.

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