More than 100 million red crabs making their annual trek from Christmas Island's rainforest to the coast are creating a migration spectacle that occupies countless bucket lists.

Their dominance of the landscape is an eye-catching phenomenon loved by tourists and treasured by residents.

For the island's conservationists, it's a reassuring sight.

Brendon Tiernan, Christmas Island National Park's senior field program co-ordinator for threatened species programs, said the war had not been won against the yellow ant invaders that threatened the red crabs.

"But we've had a significant impact," he said.

Malaysian micro-wasps were brought in by scientists in 2016 to target a preferred food source of the ants.

They've helped manage the pests, which are highly territorial and spray formic acid

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