These ancient creatures have bright blue blood! It contains a special ingredient that helps doctors make sure vaccines and medicines are safe from germs. It's so precious it costs $15,000 per liter!

Long before dinosaurs roamed the Earth, horseshoe crabs were already swimming in our oceans. Today, they are "living fossils" with a secret weapon inside them: bright blue blood that acts like a biological alarm system.
Unlike humans, whose blood is red because of iron (hemoglobin), horseshoe crab blood uses copper (hemocyanin) to carry oxygen. When copper meets oxygen, it turns blue, just like how old copper statues turn green!
The real value lies in a special cell called LAL (Limulus Amebocyte Lysate). This cell is incredibly sensitive to bacteria.
Horseshoe crabs are the silent guardians of modern medicine. Their alien-looking blue blood is the gold standard for keeping our injectable medicines safe from dangerous germs.