Motility of small nematodes in disordered wet granular media

TL;DR

This study explores how small nematodes move in wet granular media, revealing that particle presence enhances propulsion and that media properties influence locomotion gait transitions.

Contribution

It uncovers the impact of particle dispersity and density on nematode motility and gait, highlighting adaptability to different granular environments.

Findings

Propulsion speed is enhanced by particles and nearly independent of area density.

Waveform changes from swimming to crawling in dense polydisperse media.

Locomotion is significantly affected by bulk material properties at high area density.

Abstract

The motility of the worm nematode \textit{Caenorhabditis elegans} is investigated in shallow, wet granular media as a function of particle size dispersity and area density ($\phi$). Surprisingly, we find that the nematode's propulsion speed is enhanced by the presence of particles in a fluid and is nearly independent of area density. The undulation speed, often used to differentiate locomotion gaits, is significantly affected by the bulk material properties of wet mono- and polydisperse granular media for $\phi \geq 0.55$. This difference is characterized by a change in the nematode's waveform from swimming to crawling in dense polydisperse media \textit{only}. This change highlights the organism's adaptability to subtle differences in local structure and response between monodisperse and polydisperse media.