Perilous Red Crab Migration | Incredible Animal Journeys | National Geographic

In the Indian Ocean, another mom said time her journey to perfection. On a tiny speck of land, monsoon rains trigger a miracle of nature. She may not look that impressive, but this little Christmas Island red crab, around the size of your hand, is on a mission to become a mom. Crabs evolved in the sea, but she's completely adapted to a life on land, almost. Her babies will only develop in saltwater.

But to get there, a five-mile trek from her home in the forest, all the way down to the beach. It's a long way on four-inch legs, especially walking sideways. At least she's got company—70 million moms and dads to be called back to the ocean once a year to breed. This big little journey can take two weeks. And on the way, there will be casualties.

Ten times her size, the largest land crab on earth, the robber crab, armed with crustacean-crushing pincers. The red crab's eyesight is so bad that it's easy to run into trouble and harder to get out alive—unless luck is on your side. But there are bigger dangers still to face.

She's got time this just right. Fortunately, on lots of roads here today, the crabs get the right of way. A million-strong march all arrive right on schedule at the beach.