Archives of The Cold Blooded News

The Newsletter of the Colorado Herpetological Society

Volume 32, Number 11;   November, 2005

Wood Turtles Stomp For Their Supper

by Martin J. Rosenberg

The forests are full of wondrous sounds. One cannot help but be amazed and overwhelmed by the melodies (or cacophony) emanating from the treetops, as we invade the homes of natives of the forest. Which brings to mind one of the most unique sounds I have ever heard in the forest (and, ultimately, the point of this story).

During my first-ever herping trip, in 1973, I found myself camped in Apalachicola National Forest in north Florida. On my first day there I was hiking through the woods, looking for snakes and enjoying the multitude of sounds produced by the birds in response to my trespassing their boundaries. Suddenly, the mellifluous tones were countered by a loud, rasping, gru-u-u-u-nt, gru-u-u-u-nt, gru-u-u-unt from deep in the forest. Curious, I left the trail and homed in toward the source of this most incongruous sound. I soon came across several young boys who were involved in one of the strangest activities I had ever witnessed. They had sunk tall, heavy wooden stakes into the ground and were rubbing the flat tops of these stakes with pieces of wood, producing the "grunting" sounds.

At first I thought they were Scouts trying to earn their fire-starting merit badges. But they quickly made their purpose known. They were "grunting" for worms. Rather astounded that I was astounded, they explained that this was a common way of collecting worms for fishing. The vibrations produced by their "grunting" caused the worms to head topside, where they could be easily collected. The bucket of worms next to each "apparatus" attested to the success of the method. And so, the innocent Yankee was taught yet another lesson in life by folks more worldly than he.

This incident sank to the lower levels of my memory bank and did not surface again until a few weeks ago, when I read a fascinating article in the December, 1986 issue of Copeia, the journal of the American Society of Ichthyologists and Herpetologists. According to an article by Dr. John Kaufmann of the Department of Zoology, University of Florida at Gainesville, fishermen are not the only creatures to use this technique.

For the past three years, Dr. Kaufmann has been conducting studies on the wood turtle (Clemmys insculpta) biology from Centre County, Pennsylvania. He has implanted transmitters into the turtles so he could find them whenever he wanted and observe their activities. According to his report, he observed many of his marked (as well as unmarked) turtles stop, stomp one or the other foot on the ground, and then eat the worm that surfaced in response to the stomping. The result of the stomping was frequent and so consistent that there seems to be no doubt that these turtles intentionally stomp on the ground to obtain their food. The technique varied from turtle to turtle, but basically it consisted of stomping once per second, first with one foot and then the other. "Stomping sessions" lasted 15 minutes or more, but some lasted over four hours. Although earthworms seemed to be the most common food item made available by this technique, small slugs and arthropods were also eaten, and were presumably brought to the surface by stomping. Usually the stomping "bout" began with a light treading by one foot, and the force increased by the eighth stomp. Some stomps were audible for several meters and sometimes the turtle's plastron would bang against the ground, adding to the force of the blow.

To confirm that the stomping did indeed bring worms to the surface, Dr. Kaufman tried to imitate the turtles by tapping on the ground with similar rhythm and force shown by the turtles. Several worms surfaced and began to crawl away. In one case, four worms emerged from a one-foot-square area of mud within 15 seconds!

Most of the stomping activity was observed along damp creek banks of the wet forest floor near creeks. The turtles stomped at all times during the day over a wide range of air temperatures.

Besides man and (now) wood turtles, the only other animals which are known to obtain worms by causing vibrations in the soil are birds. Gulls are known to do this, and similar behavior has been seen in several other kinds of birds, but it has not been established that this behavior is directed at obtaining earthworms, except in the gulls.