Animals move through their environments by selecting
gaits that are adapted to the physical nature of their
surroundings. The nematode Caenorhabditis elegans swims
through fluids or crawls on surfaces by propagating
flexural waves along its slender body and offers a unique
opportunity for detailed analysis of locomotory gait at
multiple levels including kinematics, biomechanics and the
molecular and physiological operation of sensory and
motor systems. Here, we study the swimming gait of C.
elegans in viscous fluids in the range 0.05–50·Pa s. We find
that the spatial form of the swimming gait does not vary
across this range of viscosities and that the temporal
frequency of the swimming gait only decreases by about
20% with every 10-fold increase in viscosity. Thus, C.
elegans swims in low gear, such that its musculature can
deliver mechanical force and power nearly 1000-fold
higher than it delivers when swimming in water. We find
that mutations that disrupt mechanosensation, or the laser
killing of specific touch receptor neurons, increase the
temporal frequency of the undulating gait, revealing a
novel effect of mechanosensory input in regulating the
putative central pattern generator that produces
locomotion. The adaptability of locomotory gait in C.
elegans may be encoded in sensory and motor systems that
allow the worm to respond to its own movement in
different physical surroundings.