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 . In particular, their large compound eyes aid in locating a mate . 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 .
Horseshoe crabs are fine soldiers. They are strong creatures, made to last as the paleontologist Richard Fortney remarked . 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 , 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 .
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 . 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 .
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 . It is estimated that 3 to 15 percent of these crabs die after being bled , while those that survive exhibit sluggish behavior . Also, scientists saw a decline in the population of horseshoe crab in Delaware, and so prompted the creation of a sanctuary . Scientists are also on the way of creating synthetic amebocytes .
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!
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 Krulwich, R. (2012, June 1).What the vampire said to the horseshoe crab: ‘your blood is blue?’ Retrieved from http://www.npr.org/sections/krulwich/2012/05/31/154095868/what-the-vampire-said-to-the-horseshoe-crab-your-blood-is-blue
 National Ocean Service (2015). Are horseshoe crabs really crabs? Retrieved from http://oceanservice.noaa.gov/facts/horseshoe-crab.html
 Mancini, M. (2015, September 21). 10 hard-shelled facts about horseshoe crabs. Mental Floss. Retrieved from http://mentalfloss.com/article/68286/10-hard-shelled-facts-about-horseshoe-crabs
 Walker, K. (2014, July 15). 10 facts about horseshoe crabs. Retrieved from http://blog.panamajack.com/10-facts-about-horseshoe-crabs/
 Jones, L. (2015, April 13). Are there some animals that have stopped evolving? BBC Earth. Retrieved from http://www.bbc.com/earth/story/20150413-can-an-animal-stop-evolving
 Moss, L. (2014, March 11). Why is horseshoe crab so vital to pharmaceuticals? Mother Nature Network. Retrieved from http://www.mnn.com/earth-matters/animals/stories/why-is-horseshoe-crab-blood-so-vital-to-pharmaceuticals
 Edgecomb, M. (2002, June 21). Horseshoe crabs remain mysteries to biologists. National Geographic. Retrieved from http://news.nationalgeographic.com/news/2002/06/0621_020621_wirehorseshoecrab_2.html