Why are There 30 Million Horseshoe Crabs on This Beach?

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.