During my first year of grad school I conducted a jailbreak– a fellow grad student and I snuck into the Invertebrate Zoology lab and freed all the horseshoe crabs. I wish we’d know then that we dropped about $50,000 back into the sea. Of course, horseshoe crabs aren’t that expensive, but their blood is. One quart of horseshoe crab blood costs around fifteen thousand dollars . And why would anyone pay for that? Well, in addition to coming in a shade of oh-so-chic blue, it also saves human lives.
Horseshoe crab’s superpower blue blood is a bacteria fighting machine, and scientists are literally borrowing this trick to help test medical injections for contamination. When a horseshoe crab is cut, the wound is immediately slathered in bacteria from its murky surroundings. To prevent a potentially lethal infection, certain blood cells carry compounds that cause the blood to clot up when exposed to bacteria fragments. Cut. Clot. Cut. Clot. The horseshoe crab is quickly sealed back up and ready to go. There it is, our horseshoe crab wallowing in a muddy pit, fighting infection and being awesome.
Now cut scene from our warm, cozy shoal to a cold, sterile lab. A scientist is cradling his head in distress. Even after sterilization, one of his vaccine batches is making people sick, causing serious complications. Little does he know that, thanks to molecules in the bacterial outer layer, these suckers can remain toxic even after death. The only way to test for the presence of bacteria pieces is to inject some adorable fluffy bunny with the vaccine and see if it gets sick.
At least, that was the only way. Bunny testing was the main way various injectables and implants were tested for contamination. Until folks realized that not only could you test with horseshoe crab blood and get near instant results, you didn’t even have to kill the crabs. Round ‘em up, wash ‘em off, give ‘em a good clean, and then extract about ⅓ of their blood. The crabs are then returned to the wild. The blood, on the other hand, is shipped off for processing, and the clotting factors isolated. If a vaccine is contaminated with bacteria, adding a bit of horseshoe crab powder will turn the solution into a gooey mess, if it’s safe, it remains liquid .
Do the crabs mind? A bit. Horseshoe crabs are roughly 10% more likely to kick the bucket in the year following bleeding, compared to their un-stuck comrades . But this, scientists suggest, isn’t really a big threat to crab populations when stacked against all the other things they have to deal with- like being used for bait . In fact, some of the same crabs may be collected for blood extraction year after year after year.
As for our escaped inmates? When we freed our Invertebrate Zoology horseshoe crabs, we thought for sure they’d return to their friends and tell them all about their terrible abduction to an alien lab. They would be shunned, the laughing stock of the horseshoe crab community. Clearly, we underestimated just how often horseshoe crabs visit our world.
The effect of heavy bleeding on mortality of the horseshoe crab, Limulus polyphemus, in the natural environment