Reversible kink instability drives ultrafast directional jumping in nematodes and soft robots.

Nematodes are abundant in most ecosystems, playing a pivotal role in soil health and nutrient recycling. One species of Entomopathogenic nematodes (EPNs), Steinernema carpocapsae, exhibits a bending-elastic instability, or kink, before becoming airborne. We discuss evidence that this kink is crucial for improving launch performance. We demonstrate the directional (forward and backward) jumping of EPNs and verify this with simulation and soft robotic model. EPNs actively modulate their aspect ratio, forming a liquid-latched closed loop over a slow timescale O (~1 s), then rapidly open it O (~10 µs), achieving heights of 20 body lengths (BL). By analyzing both jumping nematodes and a bio-inspired Soft Jumping Model (SoftJM), we explore the mechanisms and implications of this kink.