Collective motion of vinegar eels: metachronal waves and induced flows

We experimentally study the collective motion of the free-swimming nematode Turbatrix Aceti also known as the vinegar eel. With a typical size of 1 mm these nematodes are evolving at intermediate Reynolds numbers where inertial, non-linear and time-dependent flows can play a significant role. We find that at high concentration they spontaneously aggregate at the borders and synchronize their beating motion, producing a striking collectively moving and oscillating metachronal wave. The flow produced by this collective state is sufficiently strong to visibly deform the surface of the liquid and displace objects in the bulk of the fluid. This novel biological system can become a model organism to study active matter at intermediate Reynolds numbers and show great promise for such applications as on-demand flows and controlled displacement of objects.