Every spring the beaches of Delaware Bay play host to one of the world’s wildest parties. Millions of prehistoric crabs (and hundreds of thousands of birds) converge here. These horseshoe crabs spend most of their lives in the ocean depths. But every May and June, their spindly little legs will carry them 60 miles or more to congregate on sandy beaches up and down the Atlantic coast. Nowhere are their numbers greater than in Delaware Bay. As many as 30 million crabs — a population the size of Sh