Droves of red crabs cause traffic jams and swarm on Christmas Island beaches in epic migration to sea

In an annual phenomenon unmatched anywhere in the world, millions of red crabs emerged from the forest on Christmas Island Tuesday, swarming over roads and beaches on their way to the sea to breed.

Every year the large crabs migrate across the Australian territory in the Indian Ocean, south of Indonesia.  

Celebrated naturalist Sir David Attenborough once filmed the event, and later described it as one of the most memorable moments of his career.

WATCH | Attenborough lets crabs crawl on him as he visits the migration event:

"This year's migration has just been absolutely epic," said Christmas Island National Park natural resource manager Brendan Tiernan.

"The roads have been a seething mass of red crabs. It's caused traffic jams on this small island and people having to get out of their cars and rake them out the way."

Nowhere else in the world does the ecological phenomenon occur on such a scale.

"Some people were quite freaked out by the fact that they're surrounded by millions of crawling arthropods, whereas other people are just immersed — basically [they] do a little red crab angel," Tiernan said. "They'll lie on ground and let themselves get covered in red crabs."

'Sometimes we call it red crab island'

According to Parks Australia, the migration starts with the first rainfall of the wet season — usually in October or November.

The red crabs time their march carefully. Their spawning is always in synch with the last quarter of the moon, so that it happens before dawn on a receding high-tide.

"Sometimes we call it red crab island,' Tiernan said. "The island's community acknowledge just how important red crabs are to our ecosystem and to our economy, to tourism."
 
The Christmas Island red crab is unique to the island and protected by Australian law.