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Worm Grunting Image 2
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Worm Grunting (Image 2)

July 12, 2010
The eastern American mole (Scalopus aquaticus Linnacus) showing the large forelimbs used to excavate tunnels. The moles have a voracious appetite that includes the earthworm (Diplocardia mississippiensis). Scientists think the vibrations made by worm grunting--accomplished by driving a wooden stake into the ground and then rubbing the top of the stake with a long piece of steel called a rooping iron, which makes a peculiar grunting sound--may mimic the sound of digging moles, causing earthworms to flee from their underground hideouts. [Image 2 of 3 related images. See Image 3.] More about this Image Ken Catania, an associate professor of biological sciences at Vanderbilt University, wanted to study the biological basis for worm grunting. Catania found that a population of the eastern American mole (Scalopus aquaticus) inhabits the area where the earthworms are collected. The earthworms have a pronounced escape response from the moles consisting of rapidly exiting their burrows to flee across the soil surface. But why, Catania wondered, do the earthworms suddenly exit their burrows in response to vibrations, thus exposing themselves to predators? Recordings of vibrations generated by bait collectors and moles suggest that "worm grunters" unknowingly mimic digging moles. An alternative possibility too is that the worms interpret the vibrations as rain, and surface to avoid drowning. However, this theory has not been supported. Previous investigations have revealed that both wood turtles and herring gulls vibrate the ground to elicit earthworm escapes, indicating that a range of predators may exploit the predator-prey relationship between earthworms and moles. In addition to revealing a novel escape response that may be widespread among soil fauna, the results show that humans have played the role of "rare predators" in exploiting the consequences of a sensory arms race. To learn more about Catania's investigation, see the Plos One story, "Worm Grunting, Fiddling, and Charming--Humans Unknowingly Mimic a Predator to Harvest Bait." [The research was funded by a MacArthur Foundation fellowship and a National Science Foundation CAREER award (IBN 02-38364).] (Date of Image: 2008)