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This year's Christmas Island red crab migration is expected to see 65 million of the critters trek from tropical rainforests to the sandy coast, according to Parks Australia.
Key points:
- Red crabs have begun their annual migration on Christmas Island
- Parks Australia says this could be one of the biggest seasons in recent years
- The crabs trek up to 20 kilometres from the rainforests to the coast
The island's native species manager Derek Ball said this year's migration could be the biggest in years.
Heavy rainfall last Saturday kicked off the species' parade throughout the island, where some roads have already been closed to give them safe passage.
Wildlife photographer and Swells Lodge owner Chris Bray said when the island woke, it was "red with crabs".
"The next morning there was millions of crabs that just came out of the burrows all across the island," he said.
The entire migration process takes about three months and begins with the journey to the coast, where the males dig a burrow to breed in.
The females stay under the sand for incubation, before releasing their eggs into the ocean when the tide is right.
Mr Ball said tens of millions of crabs were already on the move.
"It's only been a few days, but it certainly looks like this is going to be a huge migration," he said.
"We do have a very large number of crabs coming down so we're keeping a very close eye on that over the next few weeks."
Pest control behind surge
Mr Ball said the crab population had rebounded in recent years due to pest control.
"Those numbers are approximately doubled from what they were five or six years ago," he said.
"That's probably largely due to the fact that we've been able to suppress invasive species like crazy ants, which do kill the crabs unfortunately."
Yellow crazy ants have killed millions of red crabs since accidentally being introduced to the island in the 1990s.
The crazy ants spray acid into the crabs' eyes and leg joints to immobilise them, before eating them.
What's it like to live on the island?
Mr Bray said witnessing the migration was "spectacular" and a major force behind the island's tourism, but the novelty did wear off after a few weeks.
"It does make life a lot harder around town to do the normal things like just drive down to the shop," he said.
"There's traffic management or the national park rangers out there with lollipop signs … forming convoys of cars to limit the flow of traffic over the crab areas
"There's so many contraptions on the island to try and give the crabs safe passage to do their thing."
Crabs part of island's 'DNA'
Will Parker has lived on Christmas Island with his family for the past year and has been mesmerised by the migration.
"It's fascinating and intriguing, there's no way so many humans could move in such … [an] orderly way," he said.
"The sound is the thing that sticks in my mind the most, millions of tapping little feet all driven by a fierce instinct to get to the ocean for the sake of the next generation."
Mr Parker said the crabs meant "everything" to Christmas Island.
"They are part of the island's fibre, it's DNA."