Proteus mirabilis swarmer cell differentiation is induced by physical conditions that inhibit rotation of vegetative swimmer cell flagella. The protein FliL is important however, signal transduction to induce differentiation is unknown. Defects in differentiation result from mutations in genes involved in cell-wall formation and flagellar genes regulations. I hypothesized that upon surface contact, torsional stress due to inhibition of filament rotation activates stress response, induces swarmer cell differentiation and passes this signal to the protein FliL through a second protein, UmoA. My results show that the expression of stress gene cpxP changed over swarming migration with highest levels at zones of initial inoculation and areas where migration stops. I also show that complementation of fliL defect is viscosity-, temperature- and wettability-dependent, and fliL cells show improved swarming migration compared to wild-type on 0.8% agar. The study gave insight on the role of cell wall stress and fliL in swarming.