  For many applications, it is important to catch collections of autonomously
navigating microbes and man-made microswimmers in a controlled way. Here we
propose an efficient trap to collectively capture self-propelled colloidal
rods. By means of computer simulation in two dimensions, we show that a static
chevron-shaped wall represents an optimal boundary for a trapping device. Its
catching efficiency can be tuned by varying the opening angle of the trap. For
increasing angles, there is a sequence of three emergent states corresponding
to partial, complete, and no trapping. A trapping `phase diagram' maps out the
trap conditions under which the capture of self-propelled particles at a given
density is rendered optimal.
