Sometimes called “living fossils,” horseshoe crabs have patrolled the world’s shallow coastal waters for more than 450 million years, outlasting the dinosaurs. But their population has cratered more than 70 percent since 2000 as a result of over-harvesting and habitat loss.

Since the 1970s, horseshoe crabs have been caught, bled alive, and returned to the sea to harvest a protein called “Factor C,” which detects endotoxins that can contaminate drugs. Their bright blue blood is used for testing the safety of biomedical products.

With helmet-like shells, spike-like tails and five pairs of legs connected to their mouths, horseshoe crabs crawl ashore along the Atlantic and Gulf coasts each spring to lay their eggs on beaches in massive spawning events.

A conservation group sued President Donald Trump’s administration on 6 January over its failure to act on protecting American horseshoe crabs (Limulus polyphemus).

“Harvesting horseshoe crabs for blood is now the number one threat to horseshoe crabs,” Will Harlan, a scientist at the Center for Biological Diversity, which brought the legal case against the National Marine Fisheries Service, told Agence France-Presse.