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Christmas Island’s Case of Crabs

It’s either the most amazing or the creepiest of scenes – millions of tiny clawed creatures scuttling across the entire ground as they make their way from the forests to the ocean, much like a carpet of red zombies that will stop at nothing to reach their goal. They will scurry across roads, patios, your foot, and anything that comes in their way – you can hear the pincers of this little red army scrape across the floor as they march.

The mighty red army

Whichever way you look at it, the great annual Red Crab migration on Christmas Island is definitely breathtaking and has to be seen to be believed. The migration happens at the onset of the wet season (usually somewhere between October and December) each year in synchronisation with the cycle of the moon. The main goal for this teeming mass is, of course, to have sex. Normally dormant in their burrows in the forest for most of the year, the rain acts as a wake-up call (or an aphrodisiac) and turns these crabs into soldiers of love.

Red Crab Highwway © CITA

It’s not that you don’t see the crabs in the dry season – they’re pretty prolific all over the island. Whether you’re hiking in the jungle, chilling out on your beach-front patio or playing a round of golf, the crabs are always there. It’s just that during rainy season, their population simply explodes.

In an instant, the jungle floor, roads, patios and the golf course all become a carpet of red. Instead of being extras at a B-grade zombie movie, they’re instantly elevated to movie-star status. There is a penalty stroke should your golf ball accidentally hit one. The school bus stops short of the school to avoid the migrating mass. Even classrooms have to have specially-designed crab boards to stop the them marching right on under the doors and filling up the classrooms. Roads have to be diverted and crab bridges have to be built specially for them.

Crab Mating
The mating scene is simple – both male and female crabs dip just briefly in the ocean and then mate in newly-dug burrows. After that, the exhausted males will return to the jungle and the females stay along the shoreline, with their eggs stuffed in a pouch under their carapace. In between the tides, the females will raise their claws to the sky and give a pelvic shake – as if to say ‘I’ve scored!’ – and wiggle out globs of eggs into the water until it turns into some sort of egg soup.

'It's MY twig!'

After about a month in the ocean, the surviving hatchlings (most will be eaten or swept away by ocean currents) gather in pools close to the shore where they grow into baby crabs. These 5mm critters will then march inland into the jungle to mature for about 4-5 years, and then crawl out of their burrows to repeat the performance of their parents.

3 Responses to “Christmas Island’s Case of Crabs”

  1. electric says:

    Really informative blog post. Will read on…

  2. league of legends says:

    I don’t know why…

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