Adhesion and Injury Cues Enhance Blackworm Capture by Freshwater Planaria

Inaquatic ecosystems, freshwater planarians (Dugesia spp.) function as predators, employing specialized adaptations for capturing live prey. This exploratory study examines the predatory interactions between the freshwater planarian Dugesia spp. and the California blackworm (Lumbriculus variegatus). Observations demonstrate that Dugesia is capable of capturing prey more than twice its own length. The predation process involves a dual adhesion mechanism whereby the planarian adheres simultaneously to the blackworm and the substrate, effectively immobilizing its prey. Despite the rapid escape response of blackworms, characterized by a helical swimming gait with alternating handedness, planarian adhesion frequently prevents successful escape, with no significant effect of worm size. Subsequently, Dugesia employs an eversible pharynx to initiate ingestion, consuming the internal tissues of the blackworm through suction. Blackworm injury significantly increased vulnerability to predation, suggesting that chemical cues from wounds may aid planarians in prey detection. This study provides insights into the biomechanics and behaviors of predation involving two interacting muscular hydrostats, highlighting the critical adaptations that enable planarians to subdue and consume relatively large, mobile prey.