Fig. 5.

(A) Schematic drawing of a bifurcation. The trail of a swimmer fills the top branch and diffuses into the bottom branch around the pillar. The bifurcation is mapped to a fixed radius polar coordinate $x=(2l/\pi )\cdot \theta$ with the origin at the top of the bifurcation and $x=l$ at its entrance. (B) Trail dispersion, characterized by the concentration profile of micellar-solubilized oil molecules $c$, approximated by 1D diffusion from a step function between reflecting boundaries, with calculated profiles for times between 0 s and 600 s. Red dotted rectangle marks the gradient at $x=l$.