Millions of Red Crabs Begin Annual Migration on Australia’s Christmas Island

by Taylor Cunningham

The annual red crab migration is in full swing on Australia’s Christmas Island, and videos are proving that the population is more than plentiful this season.

Each year, the brightly-colored crustaceans leave their burrows in the rainforest and head to the coast to mate. And as always, the event puts entire towns on pause.

According to Parks Australia, the long walk begins after the first rainfall of the wet season, which usually happens in October or November. On rare occasions, the rainfall doesn’t happen until late December or early January.

The migration leads to millions of crabs crossing streets and property. Males always forge the path and females join them along the way.

Christmas Island Red Crabs Migrate Around Moon Phases

Interestingly, scientists can predict the exact time and speed of the event based on the phase of the moon. Red crabs always spawn on a receding high tide before dawn during the last quarter of the moon. And somehow, the creatures know exactly when to leave their burrows in order to get to the water on time.

The timing of the first rain determines how fast they’ll walk. If the rain comes close to their breeding date, they’ll have to make haste. If the rain comes early, they’ll take their time. And if the weather comes too late, the crabs will have to postpone their date and wait for the next month’s lunar target.

The male crabs will get to the beach first and dig burrows. Once the deed is done, they’ll return to the forest, which means the roads will be covered once more.

While the males are making their way back to the rainforest, the females will remain in the borrows and lay up to 100,000 eggs each. Then, the ladies will wait until the last quarter of the moon when the tide begins to turn before dawn. With that, they will release their many eggs into the ocean, and the larvae will begin hatching the second it they touch the water.

As expected, most of the eggs won’t survive. The lucky few that do will stick around the water and grow in small pools for about a month. Then, when they’re strong enough, they will join their fellow red crabs in the rainforest. When they do, they will take a nine-day hike inland.

Once the new crabs are safely back in the forest, Christmas Island will get a break, and the new crabs will stay hidden in rocky and under debris for the first three years of their lives before they start making the annual trip to the ocean, too.