(A) Velocity autocorrelation. (A1), From experiments with body wall muscle-tracked single worms on circular food patches; (A2), From experiments with 40 worms, of which a few were body wall muscle-tracked to allow acquisition of longer trajectories; (A3), From simulated, non-interacting worms undergoing a persistent random walk for different parameter values of η, the strength of the angular noise. The dashed line shows a value of 0.23, corresponding approximately to the expected correlation for choosing angles at random, uniformly distributed between −3/4π and 3/4π, thus representing an almost complete reorientation with respect to the original direction of motion. Note that this level is reached after about 15 s for η = 0.05 and for single worms (A1), and after about 8 s for η = 0.08 and interacting worms (A2). (B) Relative reversal rates at various local densities from experiments (solid lines and shaded 95% confidence interval, same data as in Figure 3B) and from model equations for reversal rates, parameterized with the mean of posterior distribution (dotted lines). (C) Speed switching rates at various local densities. (C1), Ratio of worms moving at fast (up to 350 μm/s) versus slow (<100 μm/s for npr-1,<50 μm/s for N2) speeds as measured in experiments; (C2), Ratio of worms moving at fast versus slow (<100 μm/s for npr-1,<50 μm/s for N2) speeds as measured in simulations with posterior mean parameters, showing average over ten (npr-1) and eight (N2) simulations, error bars showing error in the mean. The disagreement may indicate that the exponential form of kf(ρ) (see Figure 5C and main text) is only a rough estimate. For (B) and (CC), inferred model parameters were converted to units of worms/mm2.