Zoology: How the velvet worm squirts slime

The slime jet of velvet worms exploits fluid forces and elasticity to oscillate faster than is possible by neuromuscular control, reports a study published in Nature Communications. This allows the worm to rapidly spray a web-like pattern of slime that it uses to catch prey and to deter threats.

Velvet worms are segmented organisms from the tropics, characterised by multiple pairs of legs and a rapidly squirting slime jet. This slime jet is one of only a few jets in the natural world that oscillates rapidly, although the precise control mechanism behind it is unknown. In contrast to other species that actively move their heads to achieve oscillating fluid jets (such as spitting cobras and spitting spiders) the velvet worm's head remains in a fixed position.

Using high-speed videography, Andres Concha and colleagues rule out the possibility that this action is the result of muscular contractions, finding that the jet's oscillation speed is greater than the worm's known muscular contractions. By examining the velvet worm's anatomy, they then develop a synthetic mechanism to mimic the exit of fluids through the oral papillae tubes.

Creating a syringe-like action out of bio-inspired soft elastic tubes, the authors find they are able to replicate the same oscillatory motion observed in the contraction of the worm's slime reservoir. Further theoretical analysis of this motion suggests it is the result of instability due to a competition between fluid inertia and elastic resistance, similar to the oscillation of an unattended garden hose when water passes through it rapidly.