Thanks to Paul S. Jenkins for the link.

Reposted from:
http://timesonline.typepad.com/environment/2008/10/secrets-of-worm.html

The secret of worm grunting, a mysterious technique used by fishermen to tempt worms to the surface, has been unearthed.

Worm grunting is popular in the United States - they even hold grunting festivals - and involves driving a wooden stake into the ground and rubbing it repeatedly with a length of steel.

To most people such behaviour might be regarded as, at best, eccentric but to fishermen it is a tried and tested means of providing enough bait to keep them going for hours.
A biologist intrigued by the practice has now established that the apparently suicidal behaviour of the worms in coming to the surface, where they are easy prey, is driven by a desperate desire to escape their deadliest of enemies - moles.

Moles are such voratious eaters of earthworms that the invertebrates would rather risk being caught by a bird or dried up by the sun than come within range of one.

Dr Ken Catania, of Vanderbilt University in the US, found that the vibrations created in the soil by rubbing steel on the stake mimicked those made by moles digging through the soil.

Fishermen had happily made use of the practice, known variously as worm grunting, tickling, snoring or charming depending on where it is done, but didn’t know why it worked.

His conclusion, reached after a series of experiments in the Apalachicola National Forest, in Florida, confirmed a remark made by Charles Darwin in his 1881 book The Formation of Vegetable Mould.

“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,” he wrote.

Dr Catania, reported his findings in the online journal PLoS ONE, after carrying out a series of experiments in Apalachicola National Forest in Florida where eastern American moles, Scalopus aquaticus linnaeus, are plentiful.

He said: “Eastern moles don’t come to the surface when they are foraging, so fleeing to the surface provides the worms both immediate safety and the most efficient means for getting away from them.

“The moles are quite noisy. Often you can hear the sounds of a mole digging in the wild from a few feet away.”

The finding supports observation of gulls and wood turtles which have suggested the animals knew that by slapping their feet on the ground they would bring worms within reach.

He found, with the help of veteran worm grunters Gary and Audrey Revell, that hundreds of earthworms came to the surface within 12 metres of the stake.

“This makes it possible for an experienced worm grunter to collect thousands of worms in a day,” he added.