For the last several years, medical researchers have been studying horseshoe crabs, especially the Atlantic horseshoe crab (Limulus polyphemus). For the record, horseshoe crabs are not true crabs; they belong to a different subphylum, Chelicerata, and are related to arachnids. They have also been around for 450 million years.
Scientists have gotten interested in their blood, which is pale blue, because of the hemocyanin that transports oxygen through the crab’s blood. Hemocyanin is copper-based, in contrast to the hemoglobin that mammals use, which is red and iron-based.
What medical researchers find so interesting about horseshoe crab blood is its anti-bacterial qualities. When a horseshoe crab suffers a bacterial infection, the amebocytes, which are analogous to our white blood cells, surround and destroy the bacterial invaders at astonishing speed. While a mammal’s white blood cells can take up to two days to fight infectious bacteria, a horseshoe crab’s amebocytes get the job done in around 45 minutes.
Naturally, scientists would love to know how the amebocytes work, so horseshoe crab blood is used extensively in medical testing and vaccine research. Unfortunately, using the blood involves catching the crabs and bleeding them dry which, of course, kills them.
To make matters worse, horseshoe crab blood is valuable. A single liter, which is slightly less than a quart, is worth $15 grand. Not surprisingly, local populations have been decimated. Although they lay thousands of eggs, it takes a horseshoe crab about 10 years to reach maturity. That means it can take time for a population to recover its numbers.
Given that, researchers have begun harvesting only one-third of the crabs’ blood and then releasing them. While the new protocol has slowed the crabs’ decline, roughly 10 to 30 percent of the crabs still don’t survive.
