Chances are you owe your life to the horseshoe crab. In the 1950s, scientists discovered that LAL (Limulus amoebocyte lysate), a clotting agent found in the critter's powder-blue blood, binds to fungi and endotoxins, coagulating into a thick gel around such invaders. The result: a simple, surefire way to detect impurities in pharmaceutical drugs and medical supplies. Here's how drug developer Charles River, one of five companies licensed by the FDA to produce and sell LAL, harvests crabs and turns their blood into tests that can detect bacteria and other contaminants at less than one part per trillion—without killing the creatures.

Photo: Andrew Tingle

1. Catch

Fishermen licensed by the Department of Natural Resources capture the crabs that have come onto the beaches in South Carolina to spawn—they just pick them up from the shallows and put them in a boat.

Photo: Andrew Tingle

2. Clean

The crabs are transported to the lab's facility in an enclosed vehicle to keep them nice and damp. Sand, barnacles, and debris are removed, and the animals are inspected for injuries. (The company doesn't bleed ailing crabs.)

Photo: Andrew Tingle

3. Rack & Bleed

Each crab is folded at its hinged carapace, and a stainless steel needle pierces the pericardium to drain the oxygenated blood that's on its way to the heart. About 100 milliliters of blood drains into a sterilized bottle.

Photo: Andrew Tingle

4. Release

The same day they're collected, the crabs are released 70 to 80 miles away from where they were caught. This ensures they aren't re-bled too soon. The animal has enough blood in its appendages to survive until it recovers.

Photo: Andrew Tingle

5. Process

The blood is centrifuged to isolate the amoebocytes. The cells are then broken down to release the coagulogen inside, which forms the basis of LAL. The value of LAL is estimated to be $15,000 per quart.

Photo: Andrew Tingle

6. Sell

Charles River sells LAL-based tests to customers who use them to vet everything from the fluid in an IV bag to medications for soldiers in the field. Two of the lab's latest portable tests are currently on the International Space Station.

Photo: Andrew Tingle