The female in question is one of a trio (1.2) of wood turtles kept in a wooden-floored enclosure measuring approximately 4' x 8'. Within the enclosure a large plastic tub (21'' x 28'' x 10'' deep) containing dirt, a few larger rocks, and a plant, has been recessed such that the edge of the tub is flush with the wooden floor. A similarly sized tub in another area of the enclosure is filled with water to act as a small pond for soaking. The male wood turtle spends a majority of his time in the water, while the females move around the enclosure to a greater extent. In addition to the three Clemmys, two box turtles (Terrapene carolina), a male and a female, are housed in the same enclosure. The land area has been used for egg deposition by the female box turtle three separate times.
At approximately 11:00 AM on August 6th, 1995, dirt from a plastic cup used to hold earthworms was emptied onto the land area in a few discrete piles (the earthworms in the cup had been fed to other turtles). This cup has been used for earthworm storage for many months, and the wood turtles appear to recognize it as a source of earthworms, as they become agitated upon seeing it, in a manner similar to that exhibited when they are presented with earthworms. One female C. insculpta moved over in front of one dirt pile and elevated her back end slightly. Keeping her left foreleg tucked in close to her shell and her right foreleg extended at a 45 degree angle away from her shell, she rocked slightly sideways, bringing her plastron down onto the ground with a thump. Contact with the ground seemed to be made by the plastron in a line extending from one front leg to the other. This thumping movement was performed about 6-10 times. Each repetition was progressively louder; the turtle elevated her rear further on the strongest thumps near the end of the cycle. At this point the turtle paused and began thrusting her extended right front leg into the ground with moderate speed. These thrusting/pawing motions lasted for 5 - 10 seconds, and then the turtle moved forward slightly (approximately 1 - 2 inches). The stomping movement was then repeated. After one repetition, the turtle seized a worm that had moved to the surface of the dirt pile and consumed it. Stomping motions, interrupted with pawing/thrusting motions, were then resumed. Eventually the turtle moved completely over the first dirt pile, flattening it entirely, and continued across the land area to a second pile. A second worm was discovered and consumed. After moving across the second dirt pile, the turtle turned around and began moving back across the land area again. The wood turtle left a noticeably flattened line of dirt behind her as she moved. The behavior lasted approximately 12 minutes, in which time the turtle moved approximately 30 inches with two reversals of direction. Two worms were discovered and consumed.
The thumping motion was ignored by the other two wood turtles. One female remained approximately two feet away during the whole period; the male was resting in the water area. However, the female box turtle followed the wood turtle, digging in the flattened dirt behind the Clemmys. The T. carolina attempted to wrest the first worm away from the wood turtle, and was partially successful.
Some points of note in this observation:
1) This behavior was exhibited in a long-term captive animal,
2) It occurred in an environment that only approximated a wild environment,
3) Other wood turtles within sight and sound ignored the stomping motions, and
4) The behavior was initiated apparently in response to a cue that was previously recognized by the turtle as a signal for the arrival of earthworms.
Stomping for earthworms has been reported previously by a number of researchers (summarized in Ernst et. al. 1994). The behavior was exhibited by turtles in a wild population of Clemmys insculpta under study in Pennsylvania (Kaufmann, 1986). The motions of the turtles initially demonstrating earthworm stomping, as described by Kaufmann, correspond well to the observed motions of the female C. insculpta described here, although there are some alterations in the exact sequence of events during a bout of stomping. Stomping has also been observed in captive-born juveniles by James Harding (Kaufmann et. al., 1988). Based on this observation, it appears that stomping is instinctual in wood turtles. However, C. insculpta is capable of modifying this in-born behavior based on acquired knowledge, as demonstrated by the female turtle's actions described above.
Ernst, C. H., J. E. Lovich, and R. W. Barbour. 1994. Turtles of the United States and Canada. Washington, D.C.: Smithsonian Institution Press.
Kaufmann, J. H. 1986. Stomping for Earthworms by Wood Turtles, Clemmys insculpta: A Newly Discovered Foraging Technique. Copeia 1986(4):1001-1004.
Kaufmann, J. H., J. H. Harding and K. N. Brewster. 1989. Worm Stomping by Wood Turtles Revisited. Bull. Chicago Herpetol. Soc. 24: 125-126.
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