This phenomenon is most happen inChristmas Island,Australia.Red migration is native to christmas island.The central plateau of christmas island is dominated by strands of raiin forest.The chrismast island has a tropical climate and experiences both a wet season(Desember to April) and dry season(May through November).
More than 120 million red crabs can be found on the rain forest floor of Christmas Island.Red crabs live alone in dirt burrows, or deep rock crevices. Crabs stay in the shade of their dwelling for most of the year. In October or November, when the wet season is about to return, crabs begin their migration to the shore. This timing coincides with the lunar cycle and the tides.
The crabs will start their migration if there is enough time for them to complete their downward migration, mate and develop eggs before the next suitable spawning date.The first action that occurs is movement of crabs to the sea. The largest mass movement of crabs takes place in this first downward migration. Males farthest inland start this movement and are progressively joined by more and more crabs (both males and females) as the movement progresses toward the sea.When the crabs arrive at the shoreline, they dip in the sea to replenish body moisture and salts


I think that is all that i can share about this passage.Thx