In another episode, we talked about the horseshoe crab, which has existed on Earth nearly unchanged for more than 400 million years. In the last 40 years, it’s become a vital player in our medical industry.

Why? It’s in their blood.

Horseshoe crab blood is copper based, not iron based like ours, which makes it blue.

It coagulates so rapidly and completely around invading pathogens, that medical researchers realized it could be used to detect pathogens for us too.

So they isolated the coagulating agent, called LAL, powdered it, and now use it to test every vaccine, intravenous drug, and medical implant for the presence of bacteria in every hospital and lab around the world today.

To get enough blood to produce the LAL, medical companies capture half a million horseshoe crabs each year when the creatures congregate for spawning. They drain about 30% of their blood and then release them.

This procedure, along with human beach encroachment and increased fishing pressure, is reducing horseshoe crab numbers worldwide.

Scientists have responded by creating a synthetic substance similar to LAL, which is starting to replace the original, and with breeding programs to rebuild populations.

If you ever find a horseshoe crab on a beach, you can lend a hand. Pick it up by its shell—never by its tail, which can harm it—put it back in the water, and thank it for its service to humans.