  The rapid squirt of a proteinaceous slime jet endows the ancient velvet worms
(Onychophora) with a unique mechanism for defense from predators and for
capturing prey by entangling them in a disordered web that immobilizes their
target. However, to date neither qualitative nor quantitative descriptions have
been provided for this unique adaptation. Here we investigate the fast
oscillatory motion of the oral papillae and the exiting liquid jet that
oscillates with frequencies $f\sim 30-60$ Hz. Using anatomical images, high
speed videography, theoretical analysis and a physical simulacrum we show that
this fast oscillatory motion is the result of an elastohydrodynamic instability
driven by the interplay between the elasticity of oral papillae and the fast
unsteady flow during squirting. Our results demonstrate how passive strategies
can be cleverly harnessed by organisms, while suggesting future oscillating
micro-fluidic devices as well as novel ways for micro and nano fiber production
using bioinspired strategies.
