http://www.abc.net.au/science/articles/2008/10/21/2396935.htm
Scientists in the US believe they’ve found the reason why worms can be charmed out of the ground.
If you drive a wooden stake into the ground and draw a flat metal rod across the top to create a deep frog-like sound, hundreds of earthworms come to the surface.
Worm charming, or grunting as it’s known in the US, is used by anglers to capture bait.
Associate Professor Ken Catania of Vanderbilt University, Tennesse believes he has an explanation for why the worms hightail it to the surface: the vibrations sound similar to those made by burrowing moles, a voracious worm predator.
Catania, who studies moles, read Charles Darwin’s statement in a book he wrote on worms: “It has often been said that if the ground is beaten or otherwise made to tremble, worms believe that they are pursued by a mole and leave their burrows.”
Others have observed certain turtles and birds tapping the ground to bring worms to the surface to eat.