How Do Worms Use Passive Roots to Climb: A Biomimetic Tangling Polymer Simulation

California blackworms (Lumbriculus variegatus), are flexible and elongated organisms capable of entangling with one another. These worms can spontaneously aggregate with each other, forming highly dense entangled worm blobs. They can interact with their environment in intricate ways that reveal essential aspects of their behaviour and adaptation. For example, they exhibit climbing behaviour when interacting with free-floating plants like duckweed (Lemna sp.) in their vicinity. The dangling roots of the duckweed provide support for the maneuvering and climbing worms. Assembly of the duckweed and worms acts like a floating raft, enabling to achieve faster collective locomotion. Drawing inspiration from this mechanism, we model the ensemble of California blackworms and duckweed as a system of active and passive polymers, respectively. In our computational description, the worm is modelled as a flexible active polymer endowed with self-propulsion and an active chiral motion making them tangle with each other. The duckweed is modelled as a polymer with finite stiffness, anchored or free at one end of the polymer. Using our computational approach, we demonstrate that the stiffness of the passive polymer and strength of the activity of the polymer are deciding factors in the climbing behaviour. We believe that our study, which explores the mechanisms behind worm locomotion and climbing behaviour, is essential for advancing the design of bio-inspired robots that can mimic these natural movements across diverse terrains.