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Myths in the Museum: Horseshoe Crabs, Blue Blood, and Modern Medicine

Marianne JDatiles7 December 2018

This is the third segment in the Myths in the Museum series; you can go back and read about the dugong and mermaid, and the narwhal and unicorn.

 

With Halloween now behind us and the golden days of autumn getting shorter and shorter, a new time of year is fast coming upon us…one filled with tissues, stuffy noses, and general misery. Flu season.

Yes, it’s that time again, when the cold frost that heralds winter comes nipping at our toes at night to suck the warmth from our bodies like the vampire that it is. Feverishly we brew our teas, cling to those hankies and wrap ourselves in our best woollies and Jon Snow faux furs in an attempt to fend off illness. Yet we ourselves are guilty of our own vampiric methods in this War of the Wheezing. Our flu shots, and basically most drugs and medical injections today, are possible because we harvest another species’ blood: Horseshoe crab blood.

 

Still from the PBS Documentary Crash (Source: The Atlantic, 2014)

 

The horseshoe crab, Limulus Polyphemus, is actually more closely related to scorpions, spiders, and mites than to crabs. Its common name is obvious; its exoskeleton is a large shell shaped like—you guessed it—a horseshoe. These strange-looking creatures have 10 eyes distributed around the shell to help them navigate their way. Don’t be fooled by the tail that looks like a stinger; it serves as a rudder while swimming, and can help the crab reorient itself when it gets flipped over. The horseshoe crab is the only species within its family, Merostomata, which means “legs attached to mouth”. Take a look at the 6 pairs of appendages on its underside, and you’ll see why.

 

Horseshoe crabs, our ‘living fossils’ (Source: PBS)

 

The blood of horseshoe crabs produces limulus amebocyte lysate (LAL), a protein that can detect the presence of endotoxins, bacteria, and other sources of contamination, which we use to render our medicines safe. This protein is found nowhere else on earth. It’s no wonder that this marvellous miracle protein would be found in the blood of horseshoe crabs; they’ve have remained virtually unchanged in the 450 million years they’ve existed. They’re literally living fossils, and yet another example of the strange mysteries of ocean life.

In the 1960s humans discovered the amazing LAL and soon after put it to use in pharmaceutical laboratories around the world. Horseshoe crabs were gathered from their native Atlantic habitats, taken to facilities, drained of up to 40% of their blood, and returned to the ocean. The problem, however, is that this method does little to track what happens to the crabs after they’ve returned to the wild, starved and injured. It is estimated that 50,000 die in the process each year; this, sadly, may be a gross underestimation.

 

Crabs collected from Delaware Bay, 1928 (Source: Delaware Public Archives)

 

Since the 1850s, Atlantic fishermen have harvested about 1.1-2 million horseshoe crabs annually to use as eel and fish bait. Once the medical industry got involved, however, horseshoe crab populations have drastically reduced, and by 2016 the species was added to the IUCN Red List.

A recent publication in June 2018 claims to have found a synthetic alternative to LAL; if true, this could mean a total turnaround for the species. And, possibly, humans may not have to rely on draining these ocean species’ blood and threaten their existence to protect ours.