Fig. 6. Finite-time Lyapunov exponent (FTLE) fields of the flow created by the model swimmer (S). Results are presented in a reference frame fixed on the swimmer; the swimmer moves from right to left in a laboratory reference frame (see Fig. 5). Top panel, time t=0; second panel, t=T/5; third panel, t=(2/5)T; bottom panel, t=(4/5)T, where T is the duration of a single swimming cycle. (A) Backward-time FTLE field. The ridge of large FTLE values (solid blue curve) identifies the attracting LCS. (B) Forward-time FTLE field. The ridge of large FTLE values (solid red curve) identifies the repelling LCS. See Movie 3 in supplementary material.