CHRISTMAS ISLAND, Australia –  A migration of millions of red crabs has begun at Christmas Island National Park. The migration happens every year after the first rain of the wet season, which usually happens in October or November, according to Christmas Island National Park’s website. Video from the national park shows the Christmas Island Red Crabs migrating toward the beach and ocean, where they will begin mating and spawning eggs. “The crabs have picked up somewhat overnight,” the camera operator says in the video. “It’s happening.” According to Christmas Island National Park, the crabs’ exact timing of migration is determined by the phase of the Moon. “Red crabs always spawn before dawn on a receding high-tide during the last quarter of the moon,” the national park’s website said.  A female red crab can produce up to 100,000 eggs, the website said. The female crabs will return to the forest after they lay their eggs, while the male red crabs return to the forest after mating, the site said. In late October, the national park began preparing for the red crab migration by installing a crab fence to help steer migrating crabs along the roadside to a point where they can cross the roads in a safer way. The annual migration of red crabs is Christmas Island’s biggest tourist attraction, the national park said.