Excitation of Faraday-like body waves in vibrated living earthworms

TL;DR

This study demonstrates that vertical vibrations can induce Faraday-like body waves in earthworms, revealing nonlinear phenomena in living organisms that could be used to explore biophysical processes.

Contribution

It provides the first experimental evidence of Faraday-like waves in living earthworms and offers a theoretical model for their excitation in liquid-filled elastic bodies.

Findings

Earthworms exhibit subharmonic Faraday-like body waves under vibration.

Theoretical model supports the experimental observations.

Potential applications in probing biophysical processes.

Abstract

Biological cells and many living organisms are mostly made of liquids and therefore, by analogy with liquid drops, they should exhibit a range of fundamental nonlinear phenomena such as the onset of standing surface waves. Here, we test four common species of earthworm to demonstrate that vertical vibration of living worms lying horizontally of a flat solid surface results in the onset of subharmonic Faraday-like body waves, which is possible because earthworms have a hydrostatic skeleton with a flexible skin and a liquid-filled body cavity. Our findings are supported by theoretical analysis based on a model of parametrically excited vibrations in liquid-filled elastic cylinders using material parameters of the worm's body reported in the literature. The ability to excite nonlinear subharmonic body waves in a living organism could be used to probe, and potentially to control, important biophysical processes such as the propagation of nerve impulses, thereby opening up avenues for addressing biological questions of fundamental impact.