The Atlantic horseshoe crab (Limulus polyphemus) can be found from Florida to Maine as well as the Yucatan Peninsula. Despite its name, the horseshoe crab is not a crab. It is a chelicerate, a subgroup of anthropods that includes spiders, sea spiders, scorpions, ticks, and mites. Horseshoe crabs predate dinosaurs, and fossils of the animals have been found dating back more than 400 million years ago.
The blue blood of horseshoe crabs contains a protein called limulus amebocyte lysate (LAL) which can detect endotoxins, bacterial substances that can cause serious illness or death in humans. Pharmaceutical companies and medical products manufacturers rely on the protein to test for bacteria in medications and on medical devices. Unfortunately, many horseshoe crabs do not survive the blood collection process. The horseshoe crab population is shrinking due to deaths caused by the biomedical industry as well as the fishing industry, which uses the animals as bait.
As the horseshoe crab population dwindles, other animals are impacted. A horseshoe crab lays about 4,000 round blue-green eggs along the coast as often as about 20 times per year. The eggs, which are high in protein, are a major part of the diets of migratory shorebirds such as ruddy turnstones, sanderlings, and red knots. The red knot (Calidris canutus rufa) is classified as "threatened" under the Endangered Species Act.
Ted-Ed. (2017, September 21). Why do we harvest horseshoe crab blood? -- Elizabeth Cox. [Video]. YouTube.
Orange Audubon Society. (2022, September 8). Red Knots and Horseshoe Crabs. [Video]. YouTube.