Salute to the Gladiators of the Sea

Have you been vaccinated recently? Well, you ought to thank our clanky fellow, a horseshoe crab, for their precious blue blood.

You might be surprised but it’s genuinely blue – it contains a copper-based molecule called hemocyanin, carrying copper [1,2]. Copper, when it oxidizes, turns bluish-green [1,3]. Meanwhile our blood utilizes hemoglobin to carry oxygen, and it has iron in it, thus the reddish color [1,3].

These ‘crabs’ are not true crabs, not even crustaceans [2,3]. In fact, they are under the subphylum Chelicerata [3,7], being more akin to scorpions and spiders than they are to crabs [2,7]. They have 10 eyes [4]. In particular, their large compound eyes aid in locating a mate [3]. Their tails may look like a weapon to be wielded against predators, but they actually use it to propel themselves in different directions [3,4] or to flip them right up when they are capsized [2,3]. You can see thousands of these ‘living fossils’ crowded in Delaware Bay every May and June, ready to mate. A female can release as much as 90,000 eggs per clutch; however, only around 10 is deemed to reach adulthood [3].

Horseshoe crabs are fine soldiers. They are strong creatures, made to last as the paleontologist Richard Fortney remarked [1]. These armored-clad creatures in the Atlantic coasts have predated the dinosaurs for more than 200 million years [2,7] – no wonder they have been through rough patches for millions of years now. Despite a big hole on the head, a lump on the thorax, or a cracked tail spike [1], no one can easily stop these 450-million-year old ‘gundams.’ [1,4].

So what helps them become almost invincible? It’s also the very reason why we get to be injected vaccines safely for four decades now [3].

It turns out that when a horseshoe crab gets wounded, its blood instantly releases an army of blood-clotting granules which seal the invading bacteria, preventing further infection [1]. Today, their blood is extensively used to test products, intravenous drugs and medical devices that come into contact with blood. Essentially, the active ingredient is a sentinel against a “negative” bacteria, which is confirmed present if the cells clot in contact with a product [1,2,4,5]. Suffice it to say, horseshoe crabs have saved millions of lives from unsanitary injections [3].

One quart of horseshoe blood is sold by Atlantic fishermen to pharmaceutical companies for an astounding $15,000, a very lucrative business with more than 600,000 ‘donors’ yearly [3,6].

If you’re wondering how they obtain the blue blood, well, these fellows are being hosed up, sucking 30% of their blood [2,3,6]. They are released back into the sea after 48 hours, dizzy after a clueless donation [3]. It is estimated that 3 to 15 percent of these crabs die after being bled [1], while those that survive exhibit sluggish behavior [3]. Also, scientists saw a decline in the population of horseshoe crab in Delaware, and so prompted the creation of a sanctuary [1]. Scientists are also on the way of creating synthetic amebocytes [3].

So next time we get an injection or take a medication, let’s recognize the sacrifice of a horseshoe crab. May more years be ever in their favor!

To know more about horseshoe crabs, visit SeaLifeBase.

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[1] Krulwich, R. (2012, June 1).What the vampire said to the horseshoe crab: ‘your blood is blue?’ Retrieved from

[2] National Ocean Service (2015). Are horseshoe crabs really crabs? Retrieved from

[3] Mancini, M. (2015, September 21). 10 hard-shelled facts about horseshoe crabs. Mental Floss. Retrieved from

[4] Walker, K. (2014, July 15). 10 facts about horseshoe crabs. Retrieved from

[5] Jones, L. (2015, April 13). Are there some animals that have stopped evolving? BBC Earth. Retrieved from

[6] Moss, L. (2014, March 11). Why is horseshoe crab so vital to pharmaceuticals? Mother Nature Network. Retrieved from

[7] Edgecomb, M. (2002, June 21). Horseshoe crabs remain mysteries to biologists. National Geographic. Retrieved from


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