Velvet worms (Onychophora) are ancient terrestrial invertebrates that have perfected a breathtakingly unique hunting mechanism. When ambushing prey, they discharge twin jets of liquid slime from oral papillae at high velocity, entangling victims in a matter of milliseconds. What confounded biophysicists for decades was how a creature with no moving mechanical parts or fast-contracting muscles could produce such wide, rapidly sweeping zig-zag spraying patterns.
High-speed video analysis revealed that velvet worms utilize an elegant passive fluidic oscillator system. The oral papillae are composed of flexible, compliant biological tissue surrounding a narrowed nozzle channel. As the worm forcibly contracts its body cavity to push the proteinaceous slime out under pressure, the fluid flow instability creates an elastic feedback loop within the flexible nozzles.
This self-sustained fluid-structure interaction causes the tips to oscillate side-to-side at frequencies up to 60 Hertz without requiring active muscle control. The expelled fluid itself is a marvel of biochemistry: a liquid mixture of disordered proteins and lipids. As the oscillating stream flies through the air and makes contact with the target, the mechanical shear stress causes the proteins to align and cross-link, rapidly transitioning the liquid into a sticky, elastic solid thread network that immobilizes prey instantly.