The horseshoe crab is what you’d get if you asked H. R. Giger to draw you an Alien Facehugger with a bulletproof vest. It’s an alien, almost evil looking creature that has probably done more for humanity than any of us could ever hope to dream.
You see, the reason the horseshoe crab looks like an armor-plated creature from millions of years ago is because it freaking totally is. According to experts, fossils of horseshoe crab ancestors date back around 400 million years and since that time, the creature has changed appearance less than a Big Mac that has been left in the sun.
Despite the horseshoe crab looking like something you’d leave in someone’s bathtub to make them move house, it’s actually pretty docile and it can be picked up without any injury to yourself or the crab. Before we continue we should note that the horseshoe crab isn’t technically a crab per se and that it’s actually more closely related to scorpions than anything in the sea. However, we’re going to refer to it as such because it makes things easier.
Moving on, thanks to the fact that these things often congregate on beaches and that they can be easily scooped up without incident, for a while, they were massively popular with farmers who liked to use them as fertiliser. The farmers would pay people to scoop up the crabs before cruelly boiling them and grinding them up as a plant food.
Luckily for the crabs, in the 60’s the awesomely named, Dr. Frederik Bang discovered that their blood had a remarkable, almost unbelievable property. When any sort of foreign bacteria was introduced to it, the blood would instantly coagulate around the bacteria, neutralizing it completely.
This means that the crab is almost totally immune to infection and disease, despite the fact it had no immune system to speak of. Dr Bang also discovered that when you injected horseshoe crab blood into another fluid, if the fluid contained dangerous bacteria, they would become immediately obvious.
This effect is massively useful in the field of medicine for detecting the presence of dangerous bacterium in things like medicine, so much so that the blood of horseshoe crabs is literally worth its weight in gold, with a quart of the blood being worth in excess of 15,000 dollars.
So how is this good for the crabs you ask? Well, as soon as scientists realised, “holy shit, this creature has magic blood” the people grinding them up for fertilizer were told to cut that shit right out. Instead the crabs began to be harvested for their blood. If that sounds worse, it actually isn’t because the process of “bleeding” the crabs is completely none lethal. To quote a guy who harvests the crabs for a living “we’re just borrowing them for a while”.
Also, as if the crab’s blood wasn’t cool enough, when it’s exposed to oxygen, instead of turning red like our blood does, it turns blue, because why the hell not.