Zoe Scott
Despite being near ethereal creatures, horseshoe crabs have something worse than a bad reputation - they have none whatsoever! With more than 450 million years of experience in their arsenal, it’s safe to say this particular species is bound to outlive us - unless we work them to the grave, that is.
Don’t believe me? These creatures have already seen the rise and fall of millions of others; breezing through the ice age and outlasting the dinosaurs with ease. Having been practically perfect for millions of years, these living fossils can be found in both museums and in the wild. They meander the North American coastline, Atlantic Ocean as well as Southeast Asia! Unfortunately, they can often be misinterpreted.
Take their name, for example; the horseshoe crab. Although labelled as a crab, they’re more closely related to arthropods such as spiders and scorpions - which means, I’m sorry to say, they won’t be making anyone’s “top ten favourite crabs” list any time soon! Being somewhat related to scorpions, you wouldn’t be wrong to assume that their sharp tail must be used for nefarious, venomous and of course dangerous purposes. But no - much like tortoises, horseshoe crabs get turned over from time to time, and their tail (or more scientifically correct, their telson) aids them in getting upright once more.
The limbs of horseshoe crabs are all rather interesting, in a way - as well as their peculiar mating habits. Picture this: you’re taking a casual stroll across the beaches of north america, it’s just turning high tide and the full moon is reflecting perfectly off of the gentle waves, or perhaps there is no moon at all - a new moon. Then all of a sudden you see movement; thousands of horseshoe crabs, making their way painstakingly up the sand using their hind appendages - their pusher legs. Females that are on average, a third bigger than the males, lead the pack - looking for a place to lay their 4,000 eggs. Males follow closely behind, the lucky ones hitching a ride off of their female counterparts - clinging on to their backs with boxing glove like front legs, unique to only males, called pedipalps; which leave marks and indents on the backs of the females which will remain for years to come. You have just witnessed the beginning of a horseshoe crabs life cycle - which will occur about 19 more times throughout spring, on only full and new moons when the tide is highest.
But after all of this, where does healthcare come in? Do these weird not-crabs really work to save lives? The answer is, of course, yes - they in fact save millions. Perhaps the most common knowledge about horseshoe crabs is their blue blood - bright blue, in fact. This is caused by copper (in chemistry, you may know it as a transition metal, which creates coloured compounds), found in an oxygen-carrying protein called hemocyanin. Hemocyanin isn’t what makes the blood of horseshoe crabs so special, however. Their ancient immune system does. Their immune cells - or limulus amebocyte lysate - are exceptionally sensitive to toxic bacteria, and when they come into contact with that bacteria, they clot around it to protect the rest of the horseshoe crab. Scientists have come to the discovery that these immune cells also detect a contaminant called endotoxins, a dangerous toxic bacteria that can have deadly results if it makes its way into vaccines and other injectable drugs.
Therefore, the logical decision was made to gather and transport horseshoe crabs to drain up to 30% of their blood so as to test the safety of vaccines - almost every vaccine has been tested with this method. Although the horseshoe crabs are released back into the wild once drained, they have shown to be more sluggish and mortality rates often rise slightly afterwards. These ancient animals are in no means endangered, but could very well be in coming years if an alternative isn’t found and used.
Thankfully, there is already an - albeit less effective - alternative. In 2016, a synthetic alternative was created, called recombinant factor C (rFC). It has been approved as an alternative in Europe and for a few U.S drug companies - although not all of America has approved its use yet, which still poses a threat to horseshoe crabs and their ecosystem.
The illusive horseshoe crab can’t exactly be paid, so they won’t be getting salaries anytime soon - but having reached the end of this article, there’s hope that they’ll at least stick around in your minds for a while yet; along with their elixir-like blue blood.
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