Bipalium adventitium Hyman, 1943, an exotic terrestrial flatworm that is predatory on earthworms, is reported from Illinois for the first time. No-choice laboratory feeding tests were performed to test the acceptability of several lumbricid earthworm species as prey for B. adventitium and to compare the mass gained by B. adventitium in feeding bouts on different species of lumbricid earthworms. All species of earthworms (Allolobophora chlorotica (Savigny, 1826), Aporrectodea rosea (Savigny, 1826), Ap. turgida (Eisen, 1874), Eisenia fetida (Savigny, 1826) and Octolasion tyrtaeum (Savigny, 1826)) presented to B. adventitium were attacked and consumed. Allolobophora chlorotica, Aporrectodea rosea and Eisenia fetida are added to the list of potential prey species of earthworms in North America. Bipalium adventitium readily attacked and fed on earthworms up to 55 times larger than themselves in mass and they gained 52% of their prefeeding live mass during feeding bouts. Prefeeding live mass of flatworms was a significant predictor of the mass gained by feeding flatworms, but prey mass was not, possibly because all flatworms fed on earthworms at least 1.9 times larger than themselves in mass. Earthworm prey species had no influence on the mass gained by feeding flatworms.