Rain, wherever it falls, life waits for it, yearns for it, and above all, moves according to its whims. Water from the skies is a reminder to all land-dwelling species that their origins were in the seas. And nowhere is this more remarkably played out than on a tiny island in the Indian Ocean called "Christmas Island".

 

Deep in the forests, far from the shores where any sensible crustacean should be, red crabs, the size of dinner plates, hear the call of the monsoon. It's time to return to the seas of their birth. With the humidity soaring, their moisture-dependent lungs can now function beyond the damp confines of the forest. The males go first, like generals at the head of a red tank division. They begin their clicking, yearly march to breed. Millions of generations have engineered these crabs for life on land, but their young must hatch in the ocean.