On a tropical island 1,500 kilometres from Australia's mainland, employers understand if you can not make it to work because of crabs on the road.

This week, Christmas Island residents are once again sharing their home with millions of the island's endemic red crabs as they begin their annual migration.

Christmas Island National Park's acting manager, Alexia Jankowski, said the season kicked off when the first rain began over the weekend.

About half of the island's 200 million crabs will leave their forest burrows and make the journey to the rocky shores to release their eggs.

The eggs then spend about a month in the ocean as larvae before they return to land as tiny crabs.

During the process, a red sea of crabs spills over the island's roads, homes and schools.

"We have to put rakes

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