Falling numbers of migratory birds awakened the wildlife authorities in the eastern U.S. to the vital role that horseshoe crabs play in feeding them on their journeys. The crabs, an ancient lineage dating back 400 million years, were caught by millions to be cut up for bait, pet food, and even fertilizer. To protect them, or to protect their cute feathered predators, catching horseshoe crabs has been restricted or banned by nearby states. The numbers of crabs coming to the beaches to mate and lay eggs have slowly begun to rise from dangerously low levels. Perhaps it’s not too late for them, if people remember to refrain from killing them.
Horseshoe crabs serve another useful purpose. They react violently to meningitis bacteria, so their blood can be used to detect it. They also have a one-step blood-clotting mechanism, so they prove that blood clotting evolved gradually over eons.
