Caenorhabditis elegans swimming in a saturated particulate system

Caenorhabditis elegans (C. elegans) is a nematode that often swims in saturated soil in nature. We investigated the locomotive behavior of C. elegans swimming in a fluid with particles of various sizes and found that the nematode swims a greater distance per undulation than it does in a fluid without particles. The Strouhal number a ratio of lateral to forward velocity of C. elegans significantly decreases in a saturated particulate medium 0.50 0.13 in comparison to a fluid without particles 1.6 0.27 . This result was unexpected due to the generally low performance of a body moving in a high drag medium. In our model, a saturated granular system is approximated as a porous medium where only the hydrodynamic forces on the body are considered. Combining these assumptions with resistive force theory, we find that a porous medium provides more asymmetric drag on a slender body, and consequently that C. elegans locomotes with a greater distance per undulation. © 2010 American Institute of Physics. doi:10.1063/1.3359611