Horseshoe crabs. The living fossils who have barely evolved since before the age of the dinosaurs likely aren’t a constant presence in your mind, but they play an important role in the medicine that keeps you healthy.
These crabs have lived on Earth in their present form for over 450 million years, living long before the dinosaurs were born, and long after the last of them died. They’ve played a fairly substantial role in human life, as they make excellent bait, and have edible eggs.
However, an alternate use for them was recently (by the crabs’ standards) discovered by Fred Bang in 1956, who found that a cell in the blood of horseshoe crabs would cause it to harden when exposed to bacteria. This cell is called an amebocyte, and serves a similar role as white blood cells do in humans. This reaction naturally serves to insulate the crabs from bacteria, but Bang realized that it could be used as an easy way to detect the presence of bacteria in medicine. This allows scientists to easily determine which batches of a product pose health risks to humans, replacing a much slower practice of experimenting on rabbits to achieve the same results.
This blood is extracted by scientists who trap crabs on the shore and extract some of their blood, before releasing them back into the waters they were taken from. Currently, there is some debate on whether this method is humane enough, as the species is considered at risk and this method unavoidably leads to death in a small number of the crabs.