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People who use vibrations to drive earthworms out of the ground to use for fishing bait may actually be mimicking the worms' natural predator, the mole.

In a worm-harvesting technique called worm grunting, people plunge a wooden stake into the earth, which they then rub with a metal stick. The grunting sound it produces brings hundreds earthworms up to the soil's surface.

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Biologist Kenneth Catania of Vanderbilt University in Nashville reports his findings in the journal PLoS ONE that he set out to study the phenomenon because it reminded him of moles, which eat earthworms while burrowing underground.

He said that when he introduced a mole into a box of wormy dirt, the earthworms fled to the surface; the mole did not follow. He also found that recordings of worm grunting and moles digging underground sounded similar.

In other words, worm grunters have been unwittingly imitating mole sounds. Worms feel the vibrations and wriggle out of the soil to avoid what they think is a fuzzy predator, but may end up on a fishhook instead.