That Crabs Are Taking a Yearly Trip
The crabs migrate every year, in tandem with the start of the rainy season, which usually begins in October or November but can lag to December or even January. Around 40 to 50 million of the island’s crabs trek across the island to reach the shoreline for mating season. While most people associate crabs with the ocean, Christmas Island is home to several terrestrial crab species that live in the lush rainforests of the 52-square-mile (135-square-kilometer) island, including the red crabs.
The crabs actually set their biological clocks for this migration to coincide with a very specific set of environmental circumstances as well as the lunar calendar. After the first rain of the rainy season, the crabs know that their optimal time for mating is during the last quarter of the moon, before dawn as the tide is going out. According to Parks Australia, this timing can change the makeup of the trip; if rains come close to the ideal spawning date, the crabs will rush across the island, but they’ll take a more leisurely road trip if they know they have some time.
