Horseshoe crabs used to be everywhere. Millions of years before dinosaurs roamed the planet, each spring, the hard-shelled creatures gathered to mate in massive mounds along the beaches of the Atlantic coast. Later, migratory shorebirds like the robin-sized red knot learned to fly up from South America to join them for a feast. The crabs’ eggs gave the birds the energy they needed to keep flying north to breed in the Arctic.
