This is one of the most colorful forces of nature and it takes place on Christmas Island in the Indian Ocean every year.
The island, named after the day it was discovered (December 25, 1643) isn't very big. More than half of it is a protected Australian national park and offers the perfect home for these little guys.
Every year, around 120 million of these crimson crabs migrate to the sea to mate. That makes the island a huge attraction for tourists.
Thousands travel to the island to get a glimpse of this red sea, which lasts several weeks.
The phenomenon actually shuts down the island so the crawlers can travel safely. A few weeks later, a wave of tiny red spawn pours back into the jungle.
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