Physical model inspired by energetic jumping nematodes

Nematodes are a taxon of microscopic worms that are more abundant than all individual animals combined. The majority of nematodes use undulatory propulsion to swim or crawl across wet conditions. Impressively, entomopathogenic nematodes which parasitize insects, are unique among roundworms because they can jump. Although the kinematics of this jumping behavior has been identified nearly 60 years ago, the energetics of elastic energy storage and release have remained unclear. Here, we utilize soft robophysical elastic structures including polymeric-based elastic cylinders and fluid-filled balloons (shells) to explore how the hydrostatic skeleton, cuticle, and muscles act as non-linear springs to store energy in the loop formation of the worm body prior to jumping. We specifically focus on the role of kinks (sharp folds) that are formed when these elastic cylindrical structures are bent beyond its buckling limit. We show that kinks in these highly deformable bodies could serve multifunctional roles: acting as a “capacitor”, enabling slow energy build-up and fast release; creating a non-linear spring for low-force, yet high energy loading; and finally offering stability during loop formation. Our study sheds insight into both how organisms exploit elastic instabilities for ultrafast motions while offering design motifs for soft jumping robots.