The red crab is by far the most obvious of the 14 species of land crabs on Christmas Island. Every year over 150 million red crabs move from inland shelters to the shore for their annual breeding season. This occurs at the beginning of the wet season (usually October/November).
That synchronized QuadriCombo of .gifs makes for a stand-alone post here, and it’s true that some crabs suddenly materialize while others disappear into vapors. More info at this awesome site – “Colors of Fauna.”