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On 25 September of this year, a warm day after a hard rain, I found several small wormlike animals creeping on the bricks and mulch in our front-yard garden. They looked like small earthworms, but with a strangely flared “head” and a black “racing stripe” down their back. They were land planarians, relatives of the freshwater flatworms call Planaria you may remember from a biology class. I had never seen these in northeastern Wisconsin. After a conversation with planarian expert Dr. Peter Ducey (State University of New York-Cortland), I learned that these are most likely Bipalium adventitium (Bipaliidae), a species introduced (accidentally, in the soil with imported plants) from temperate eastern Asia. It is a voracious predator of earthworms, which in our part of Wisconsin are also introduced from elsewhere. At the same place on October 3 rd (also after a rainstorm the night before), my wife and I observed several of these flatworms feeding together on a dead earthworm about ten times the size of the flatworms.

The species was first found in the U.S. in California in 1943, and has since been reported from Washington, northeastern U.S. states, Tennessee, and, recently, Urbana Illinois. According to Dr. Ducey, these observations seem to be the northernmost in the Midwest. If you see any yourself, let us know!

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Last updated on April 15, 2014