The effects of fluid viscosity on undulating swimmers

The swimming behavior of the nematode \emph{C. elegans} ($L\approx$~1 mm) as a function of the surrounding fluid viscosity $\mu$ is investigated using both particle- and nematode-tracking methods. Nematode tracking data show that \emph{C. elegans} move in a highly periodic fashion characterized by traveling waves. The nematode swimming speed $U$ decays nonlinearly with increasing fluid viscosity such that $U\sim \mu^{-0.2}$. Velocimetry data shows flow re- circulation regions along the nematode's body. The velocity profiles measured in the direction normal to the swimming nematode show a decay that is similar for fluid viscosities ranging from from 1 cP to 20 cP. The normalized velocity decays follow a single mater curve with $d/L$ as the independent variable, where $d$ is the normal distance from the swimming nematode. This result suggests that \emph{C. elegans} may be a good canditate to investigate low Re locomotion.