  There is a recent surge of interest in the behavior of active particles that
can at the same time align their direction of movement and synchronize their
oscillations, known as swarmalators. While theoretical and numerical models of
such systems are now abundant, no real-life examples have been shown to date.
We present an experimental investigation of the collective motion of the
nematode Turbatrix aceti that self-propel by body undulation. We discover that
these nematodes can synchronize their body oscillations, forming striking
traveling metachronal waves, which produces strong fluid flows. We uncover that
the location and strength of this collective state can be controlled through
the shape of the confining structure; in our case the contact angle of a
droplet. This opens a way for producing controlled work such as on-demand flows
or displacement of objects. We illustrate this by showing that the force
generated by this state is sufficient to change the physics of evaporation of
fluid droplets, by counteracting the surface-tension force, which allow us to
estimate its strength. The relatively large size and ease of culture make
Turbatrix aceti a promising model organism for experimental investigation of
swarming and oscillating active matter capable of producing controllable work.
