Natural History Observations on Bipalium cf. vagum Jones and Sterrer (Platyhelminthes: Tricladida), a Terrestrial Broadhead Planarian New to North America

An increasing number of exotic terrestrial planarian species have established populations worldwide. In North America, the most prominent invasive flatworms are three members of the broadhead planarian genus Bipalium. Herein we report observations on the morphology, predatory behavior, and reproduction of Bipalium cf. vagum, new to this continent and report its occurrence in Florida and Texas. Individuals of this species have a distinctive combination of head shape and pattern of dark dorsal pigmentation (large head spots, complete collar, and prominent median stripe) that distinguishes them from other members of the genus. Although the other North American species of Bipalium feed on earthworms, B. cf. vagum feeds exclusively on terrestrial mollusks. Their predatory behavior includes following mucus trails and subduing the prey by capping the prey's head with the flatworm's anterior end and wrapping the prey's foot in the body of the planarian. Members of this species reproduce via egg capsules that contain small numbers of offspring. Because this is the first land planarian reported in North America that is a predator of mollusks, native land snails and slugs are unlikely to have effective defenses against it. Therefore, we should continue to monitor its geographic spread and potential ecological impact.