Red Crab Migration Begins On Christmas Island - Number Boosted After Scientists Take On Invasive Ants

The welcome mat has been rolled out for scores of red crabs as they make their annual coastal dash on Christmas Island. Each year, the first substantial rain of the wet season triggers tens of millions of adult red crabs to leave their forest homes, in the interior of the island, and march towards the coast to mate and spawn. Christmas Island is 1,500km from the Australian mainland and lies 350km south of the Indonesian island of Java.

Staff at the Christmas Island national park have spent months preparing for the mass migration, setting up kilometres of temporary roadside barriers to channel the migrating crabs to the safety of underpasses and overpasses. They also divert traffic away from the crabs as they scurry to the coast. The park manager, Derek Ball, said the red crab was the island’s keystone species and the entire community pitches in to facilitate the “fascinating phenomenon”.

“Over many years we’ve also targeted the red crab’s biggest threat, the invasive yellow crazy ant,” he said in a statement on Sunday.

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Crazy ants were first detected on the island in the 1920s, but it wasn’t until the first super colonies formed in the late 1980s that they became a problem. The ants have killed tens of millions of red crabs over the years by spraying them with potent formic acid. But there are fewer of the invaders now after scientists deployed a micro-wasp to prey on an insect that historically provided the ants with an abundant food source.

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https://www.theguardian.com/australia-news/2023/dec/24/march-of-the-red-crabs-months-of-preparation-for-annual-mass-migration-on-christmas-island