Figure 1. Worm grunting demonstrated and described.

A. Gary Revell, a professional bait collector, demonstrates worm grunting at the Annual Worm Grunting Festival in Sopchoppy Florida on April 12 of 2008. See movie S1 for an example of worm grunting during bait collection. B. This technique requires a wooden stake and a flat piece of iron. The stake is driven into the ground and the iron is rubbed across the surface as in plate A. C. A two second recording of worm grunting vibrations made with a vertically oriented geophone at a distance of 5 meters (supplementary audio file S1). Two strokes were made during the two seconds, each lasting roughly 400 milliseconds. D, E. The relative amplitude of vibrations recorded at successive 1-meter intervals from the vibrating stake. Units are arbitrary but all recording parameters were constant throughout the study. The intensity of the horizontally recorded vibrations (n = 5) was stronger than vertically recorded vibrations (n = 3). Bars are standard error of the mean.