Science
Why is horseshoe crab blood so valuable?
- It detects bacterial contamination
- It clots wounds
- It is rare
The answer is It detects bacterial contamination. It reacts to bacterial toxins at parts per trillion - it tests every injectable drug.
Because it detects bacterial contamination at concentrations nothing else can reach. Horseshoe crabs have no antibodies; instead their blood cells clot violently in the presence of bacterial endotoxin, and that reaction was turned into a test - limulus amebocyte lysate - sensitive to parts per trillion. It is the standard safety check for injectable drugs, vaccines, implants and surgical equipment. Essentially every injection anyone has ever had was cleared by it.
The blood is blue, because it carries oxygen on copper rather than iron, and the animal is not a crab - it is closer to spiders and scorpions, and the body plan has barely changed in something like 450 million years.
The harvest is genuinely contested. Hundreds of thousands are caught each year, bled of about a third of their volume and returned to the sea; industry figures put mortality afterwards at a few per cent, independent studies have found up to about a third, and survivors appear to breed less. A synthetic alternative exists and is accepted in Europe, and the American argument is now about how fast to switch rather than whether the substitute works. Migrating red knots, which depend on horseshoe crab eggs to refuel, have declined alongside them.