Chance Observation of Escape Behavior of a lumbricid Earthworm, Aporrectodea caliginosa.

Owen J. [Sexton.sup.*]

Abstract: An observation suggests that the earthworm (Aporrectodea caliginosa) can escape predation by the eastern mole (Scalopus aquaticus) by emerging from leaf litter and traveling across its surface.

Although the diet of moles (Mammalia: Soricidae) has long been known to include earthworms (Oligochaeta: Lumbricidae) as a major component (German & Stone, 1990), there is little information available about the escape responses of earthworms in the presence of these predators (Hendrix, 1995). A serendipitous backyard observation of such as interaction seems noteworthy.

The eastern mole (Scalopus aquaticus) is native to much of the eastern United State (Burt & Grossenheider, 1976) and has become adapted to yards and gardens (Schwartz and Schwartz, 1959). An introduced European earthworm [Aporrectodea caliginosa (=C. furgida)] (Schwert, 1990) has also become adapted to North American backyards (Schwert, 1990). The earthworm was identified by one of us (D.J.). We are grateful to V.C. Hubbard of the Soil Microbiology Laboratory, University of Missouri, Columbia, Missouri and Professors James, Maharishi University, Fairfield, Iowa for verification.

Serendipitously, one of us (O.J.S.) observed a predator-prey encounter between the above two species at 1330 on the sunny, warm (24[degrees]) day of 15 May 1995 in St. Louis County, Missouri, U.S.A. The encounter took place in a fenced, raised vegetable garden in which the soil was covered with 2.5 cm of oak leaf mulch. As OJS entered the garden, he noticed that a mole was causing an upheaval of the soil and leaf litter as it moved forward 15 cm over a 2-minute period. Eleven A. caliginosa emerged in front of the displacement.

They crawled rapidly away from it over an arc of 270[degrees] and reentered the soil about 50 cm from their emergence point. None of the worms were attacked by the mole. No other earthworms were observed elsewhere on the litter surface of the garden which strongly suggests that the observed movement of the earthworms was a behavior utilized by A. caliginosa to escape predation by S. aquaticus. The intensity of the escape behavior is emphasized by the fact that the earthworms emerged under the clear sky of warm May day. One possible stimulus which initiated this escape behavior is the vibration within the upper soil and litter caused by mole's activity. Scent is another possible stimulus.

Literature Cited

Burt, W.H. and R.P. Grossenheider. 1976. A field guide to the mammals. Houghton Mifflin Company. Boston, MA. 289 pp.

Gorman, M.L. and R. D. Stone. 1990. The natural history of moles. Comstock Publishing Associates. Ithaca, NY 138 pp.

Hendrix, P.F. (ed.). 1995. Earthworm ecology and biogeography in North America. Lewis Publishers. Boca Raton, FL. 244 pp.

Schwert, D.P. 1990. Oligochaeta: Lumbricidae, p. 341-356. In: D.L. Dindal (ed.). Soil Biology Gude. Wiley Interscience (John Wiley & Sons, Publisher). New York, NY.