These are several videos capturing the annual migration of millions and millions of tiny red crabs across Christmas Island, near Indonesia. Once a year in October/November the entire population migrates from the forests to the coast to bang each other on the beach and make babies. How romantic. UH UH UH UH UH (That's the sound of crabs humping).
Keep going for three portrait-mode videos (the last one is my favorite).
Thanks to HK, who agrees it would take just about the entire population to make a decent crab feast.