This article was taken from the August 2011 issue of Wired magazine. Be the first to read Wired's articles in print before they're posted online, and get your hands on loads of additional content by subscribing online.

Chances are you owe your life to the horseshoe crab. In the 50s, scientists discovered that LAL (Limulus amoebocyte lysate), a clotting agent found in the critter's blue blood, binds to fungi and endotoxins, coagulating into a gel around such invaders. The result: a simple way to detect impurities in pharmaceutical drugs. Here's how drug developer Charles River harvests crabs (and their blood) without killing them.

Wired explains how the process works, in pictures. Enter the gallery to learn...