Yearly Christmas Island Red Crab Migration Is an Alien Event

With so much in the news about exoplanetsOpens in a new tab and UFO sightingsOpens in a new tab, it’s easy to forget the ocean and its shores are full of things that seem genuinely alien. So very many thingsOpens in a new tab. The red crabs of Christmas Island are no exception, with a yearly migration that sees the creatures go through their mating process according to the lunar phases of the Moon. And the sight can only be described as an Invasion of the Crabs!

Boing BoingOpens in a new tab reported on the Christmas Island crab phenomenon, which is the result of a reproduction process with clockwork precision. Every year the red crabs on the island—which is in the Indian Ocean north of Australia—leave their homes on terra firma at the same time. They then start marching towards the ocean to mate and spawn. The phase of the moon—that is, whether the Moon’s waxing or waning according to the way it points toward the SunOpens in a new tab—determines when the crabs begin their spawning. As well as when they end, after they’ve sent hundreds of millions of larvae into the ocean.

“The exact timing and speed of the migration is determined by the phase of the moon,” Parks AustraliaOpens in a new tab notes. “Red crabs always spawn before dawn on a receding high-tide during the last quarter of the moon. Incredibly, they know exactly when to leave their burrows to make this lunar date.”

Unfortunately, while the migrations happen every year, the crabs’ offspring’s survival rate is slim. Parks Australia says that most years no or very few baby crabs emerge from the ocean. This year, however, hopefully luck will bring in quite a hall. More than 100 million crabs are currently on their way to mate by the ocean and pass on their DNA. And we’re rooting for a downright frightening Invasion of the Crabs! sequel.