Christmas Island, a territory of Australia, sits in the Indian Ocean. In addition to the spectacular scenery of the island and the azure water surrounding it, Christmas Island is known for its crabs. More specifically, for the migration of millions of red crabs every year.
These crabs spend most of their lives inland and underground in the forest, feeding on decaying leaves. Yet once the wet season begins (usually in October or November), the crabs start their migration to the sea to mate and spawn. Their march is also dictated by the moon. They want to reach the ocean to spawn before the sun starts to rise, on an ebbing high-tide, during the moon’s last quarter. Somehow they know when it’s time to leave the nest and start the trek! Each female carries 100,000 eggs that she must shed into the sea. The only problem? While she’s a crab, she can’t swim. The goal is to release the eggs at the shoreline without being swept away by a wave.
There are an estimated 50 million red crabs on the island. Therefore, when they begin their migration, the ground, roads, bridges, and shorelines are literally swarming with crabs. In the words of Sir David Attenborough, “It is like a great scarlet curtain moving down the cliffs and rocks toward the sea.” To protect the crabs, some roads are closed during migration, and crab bridges have been built to usher the crabs up and over the road safely.