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PRI's Environmental News Magazine

Almanac: Crab Invasion

Air Date: Week of October 5, 2001

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This week, facts about the Christmas Island crab invasion. Every year at this time, the small island territory of Australia is taken over by swarms of red crabs.

Transcript

CURWOOD: It's Living on Earth. I'm Steve Curwood.

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CURWOOD: In the middle of the Indian Ocean sits the tiny Australian territory called Christmas Island, and if you happen to be there at this time of year, watch your toes, because it's the invasion of the red crabs. An army of 100 million snapping critters takes over the island during mating season. The crabs spend most of the year in extremely humid mountain rainforests on the island, but they need to lay their eggs in the ocean. So, during the October rainy season things get crazy as they all come down from the hills at once. The crabs mate in burrows near the shore and the females drop their eggs into the surf. The baby crabs hatch and live near the water for three years before they, too, make the trek uphill, to live in the forest.

Recently, though, there's been trouble for the crabs. An ant that colonists accidentally brought to the island a hundred years ago threatens them. The ants kill the crabs and take over their nests. So, the crabs are now protected. And that's probably why they outnumber the island's 900 humans 100,000 to one.

During mating season streets are closed and special migration tunnels are dug under roadways so the crabs don't get squashed. On the main pathways every inch of land is crab-covered. Most of the island's residents survive the month long ordeal by keeping their doors closed, which tends to make some of them a little crabby. And that's this week's Living on Earth Almanac.

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