The red crab   lives on Christmas Island in the Indian Ocean and has been found nowhere else in the world. But on its homeland it is a very significant species -- some 120 million individuals cover the rain forest floor and play a major role in determining the structure of the ecosystem. These large crabs are active during the day but prefer to stay in the shade and can die in the heat of direct sunlight. They feed on fallen leaves, seeds, fruits and flowers, recycling nutrients and helping to determine the spread and composition of native plants. Most of the year the red crabs live in the holes they dig throughout the forest. During the dry season they hide in these shelters to keep their body wet and remain there for two to three months. But when wet season returns in October or November they begin a legendary mass migration to their seaside breeding    grounds, moving in color1ful wave that wash over all obstacles like roads (including special passages and some closed roads built for the red crab) and even seaside cliffs. The annual migration is also closely tied to the lunar schedule. The crabs arrive at the coast and breed at such a time that the females can produce eggs and develop them in caves for a dozen or so days before carrying them into the sea exactly when high tide turns between the last quarter and new moon. During this period sea level on the beaches varies the least and offers an easier approach, which is so important that if the weather delays the migration crabs will put off laying eggs until the next lunar month. Red crab eggs grow right away, and the young live in the sea for a month before returning to the coast, changing into air breathers, and slowly returning inland to begin the cycle once again. What's important for the red crab to reproduce their young?
The right caves. The number of the crabs. The movement of the moon. The temperature of the tide.