Meghan Owings plucks a horseshoe crab out of a tank and bends its helmet-shaped shell in half to reveal a soft white membrane. Owings inserts a needle and draws a bit of blood. “See how blue it is,” she says, holding the syringe up to the light. It really is. The liquid shines cerulean in the tube.
When she’s done with the show and tell, Owings squirts the contents of the syringe back into the tank. I gasp. “That’s thousands of dollars!” I exclaim, and can’t help but think of the scene in Annie Hall when Woody Allen is trying cocaine for the first time and accidentally sneezes, blowing the coke everywhere.
I’m not crazy for my concern. The cost of crab blood has been quoted as high as $15,000 per quart.
Their distinctive blue blood is used to detect dangerous Gram-negative bacteria such as E. coli in injectable drugs such as insulin, implantable medical devices such as knee replacements, and hospital instruments such as scalpels and IVs. Components of this crab blood have a unique and invaluable talent for finding infection, and that has driven up an insatiable demand. Every year the medical testing industry catches a half-million horseshoe crabs to sample their blood.
But that demand cannot climb forever. There’s a growing concern among scientists that the biomedical industry’s bleeding of these crabs may be endangering a creature that’s been around since dinosaur days. There are currently no quotas on how many crabs one can bleed because biomedical laboratories drain only a third of the crab’s blood, then put them back into the water, alive. But no one really knows what happens to the crabs once they’re slipped back into the sea. Do they survive? Are they ever the same?
Horseshoe crab blood is an E. coli detective.
Scientists use the precious substance—specifically, the crab blood’s clotting agent—to make a concoction called Limulus Amoebocyte Lysate (LAL). LAL is used to detect Gram-negative bacteria like Escherichia coli (“E. coli“), which can wreak havoc on humans.
Basically, you can divide the bacteria of the world into two groups based on a test developed by Christian Gram, a Danish physician of the late 1800s. The two classes differ physiologically, especially in the composition of their cell walls. Gram-negative bacteria like E. coli contain a type of sugar called an endotoxin in their cell walls, while Gram-positive types like Staphylococcus (of the Staph infection) do not. (The “positive” and “negative” refer to how the microorganisms reacts to a staining test Gram invented.)