A horseshoe crab (bottom) and its blood (upper right).

One of the most expensive substances on the planet comes from one of it’s unlikeliest — and ugliest — sources: the horseshoe crab. The bright blue blood of the of these inhabitants of shallow ocean waters fetches an astonishing $60,000 per gallon. With one gallon containing 75,708 drops, this equates to each drop of blood being worth 79 cents.

What makes this weird-looking substance from a weird-looking creature so weirdly valuable?

A horseshoe crab’s immune system is super-charged to help it cope with the high risk of infection in its shallow-water environment. The result of this is that when its blood is exposed to bacteria, the defensive cells in the bloodstream immediately surround the invading contamination and isolate it to prevent it spreading.

Medical hygienists have capitalized upon this remarkable feature and use the blood of the horseshoe crab to detect endotoxins that otherwise would escape detection. So sensitive is the horseshoe crab’s blood to bacteria that it can detect and isolate a threat the equivalent size of  a grain of sand in a swimming pool.

“Detection is down to one part per trillion,” said John Dubczak, General Manager at Charles River Laboratories, “but we can take it down to a tenth of a trillion, and further orders of magnitude more sensitive.”

Countless human lives have been saved through this process, but the cost to the horseshoe crab is less beneficial. Each year over 600,000 crabs “donate” about one-third of their blood to a $50,000,000 per year industry. Between 10 and 30 percent of crabs die in the process.

In the past 15 years the horseshoe crab population in the Delaware Bay — the location of the world’s largest population of the crabs — has dropped by 75-90%.

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