Motility of swarmer cells as a function of viscosity in viscous and viscoelastic media. The three types of symbols represent wild-type (wt), Δpilin (deltaP), and SB3860 (3860) strains, in glycerol (solid symbols, with corresponding weight percentages listed on Table 1) and PEG 35000 (empty symbols, with corresponding weight percentages noted on the upper axis). The swarmer cells were counted using videos captured a few minutes after mixing with either pure glycerol or a concentrated PEG solution. The numbers of cells counted were, in PEG 35000, 4639 for wild-type, 4035 for Δpilin, and 5884 for SB3860; and in glycerol, 7174 for wild-type, 3509 for Δpilin, and 3603 for SB3860. The error bars, some smaller than the symbols, are standard errors of three separate sets of measurements.