MELBOURNE, Australia (AP) -- Killer ants on Christmas Island in the Indian Ocean are reported to be decimating the island's world-renowned crab population.

The "crazy ant" -- so-called because of its frenetic movements -- was attacking the famed red crab population at a phenomenal rate Monash University ecologist Dennis O'Dowd said Friday."I have never seen a single invader have so much impact in such a short time," said O'Dowd, one of several researchers on a long-term study of the crabs.

The crazy ant, or anoplolepis gracilipes, is believed to have been introduced to Christmas Island by west African traders about 50 years ago. About 100 million red crabs, some weighing up to a pound, live on the island, which is an Australian territory. Two-thirds of the island is national park.

In the past 18 months, the ants have attacked the crabs, killing about 3 million. The ants burrow into the forest floor and underground into the crab burrows and kill them and eat them.

O'Dowd said the sudden carnage by the ants was a mystery.