Injectable drugs are still tested with horseshoe crab blood

In the 1950s, Johns Hopkins scientist Frederick Bang noticed that horseshoe crab blood clumped into a solid gel whenever it touched certain bacteria. Jack Levin traced the reaction to bacterial endotoxin itself and turned the crab's blood cells into a detection tool.

Levin and Bang showed that even trace amounts of endotoxin triggered the clotting cascade in the blood cells of Limulus polyphemus, the Atlantic horseshoe crab, a lineage of marine animal that predates the dinosaurs by roughly 200 million years. Their 1964 paper described the chemistry behind what became known as the Limulus amebocyte lysate test.

That test, now called LAL, became the standard global method for screening injectable drugs and vaccines for bacterial contamination, replacing a slower rabbit-based test that had been used for decades. Most injectable medicine is still checked with blood drawn from live horseshoe crabs, which are bled and released, though synthetic versions are gaining ground, and the pharmaceutical industry's growing demand for that blood has become a conservation concern for the species.

A living fossil still guards most vials.