Answer:
woahh, i didn't even know that
Explanation:
i searched it up and :
"What is the horseshoe crabs blue blood used for?
Horseshoe crab blood is bright blue. It contains important immune cells that are exceptionally sensitive to toxic bacteria. ... Scientists used these clever blood cells to develop a test called Limulus Amebocyte Lysate, or LAL, which checks new vaccines for contamination."