Why is this Philadelphia beach covered with 30 million horseshoe crabs?

When spring comes to Philadelphia's Delaware Bay, the shore becomes covered with tens of millions of horseshoe crabs. It's spawning season. Learn more about this oceanic orgy in the Deep Look video above. The transcript reads like poetry:

When a female finds a good spot, she digs and digs into the wet sand.

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from Boing Boing https://ift.tt/2Wz0K6M