Successful Invasion of New York State by the Terrestrial Flatworm, Bipalium adventitium

The terrestrial planarian Bipalium adventitium Hyman, 1943, a predator of earthworms, was first identified in the United States about a half century ago and is believed to have been introduced from Asia. Since that time, anecdotal reports have indicated its presence in six states and have suggested that the flatworm may spread via human activities. To better understand the potential threat posed by B. adventitium, we investigated the extent of its dispersal in New York State, its current distribution in relation to human land-use patterns, its reproductive modes, and its predation on local earthworm species. We found specimens of B. adventitium in 13 counties of New York State. Their abundance in urban/suburban gardens and lawns suggests that dispersal has been primarily passive, by transport with the roots of replanted trees, bushes, or grasses. They reproduce both sexually, producing egg cases, and asexually, via fragmentation. They aggressively preyed on all species of earthworms that were offered, often attacking and consuming earthworms many times their mass. Its rapid spread, successful reproduction, and effective predation on many local earthworm species indicate that B. adventitium may represent a significant threat to soil ecosystems in the Northeast.