The daring 5-mile (8-kilometer) migration of Christmas Island’s adult red crabs begins with the wet season’s arrival in October or November. The crabs’ goal: move from the forest to the beaches en masse, breed, drop their eggs into the water, just before the turn of the high tide, and then return to center of the island.

This massive move of 50 million creatures is a spectacular sight. It’s also a challenge to keep them safe. As shown in the video above, Christmas Island National Park rangers do an immense amount of work to protect these animals as they traverse the roads that cross their path: cleaning up debris, constructing temporary fences, raking crabs across roads to avoid traffic, and closing some roads are all a part of the job.

There are more crabs crawling around in the archives, including migrating horseshoe crabs, a mass migration of Caribbean hermit crabs, and what it looks like when the Christmas Island red crab larvae hatch and head back for dry land.