[grunting noises]

Narrator: This is called worm grunting or roouping. And Gary Revell’s family has harvested earthworms this way for generations here in Florida’s Apalachicola National Forest. Revell draws a ten-pound steel bar back and forth across a cherry wood stoball and plays it like a giant fiddle. You can feel the vibrations 20 feet away. On the right day in the right spot and before the sun gets too high, the Revells can collect 3,000 earthworms in about three hours. And they sell every one of them to anglers who prefer wild worms.

Gary: I said, once you make the right music, they'll go to dancing for you. Hopefully I'm doing it.

Narrator: Revell knows that this music will make the worms dance, but until recently he never knew why. And it’s got less to do with dancing than running, running for your life. 

Ken: So the worms come out of the ground and travel across the surface to get away from the mole. And they’re going about as fast as I think a worm could go.

Narrator: The eastern mole was one of the worm’s most voracious predators. And it turns out that the sound a mole makes is very similar to the sound produced by worm grunters. Maybe not to the human ear, but to worms they’re one and the same.

Ken: When you put a digging mole in an arena full of worms, you get what I would describe as a running worm.

Narrator: Researcher Ken Catania studied the Revell’s methods. H, he set out to prove his theory, first suggested by Charles Darwin, that worm grunting is an example of something called exploitive mimicry. Wood turtles and seagulls do the same thing. They thump the ground imitating an approaching mole.

Woman: Set ‘em in the shade.

Narrator: Exploitive mimicry may be the scientific term, but exploitive is hardly a word that describes the Revells. They live pretty much off the grid, but wouldn't put it that way, rather outside of town where it’s quiet and the living is easy. The truth is they work like the devil.

Woman: 500 worms, that’s a full can.

Narrator: But the Revells can rest easy about living off the land. Catania says there are so few grunters compared to the number of moles in the forest, that harvesting the worms will not put much of a dent in the population or upset the balance of nature. For Assignment Earth this is Bruce Burkhardt.