Proteus mirabilis adapt their motility machinery to their environment. In liquid, the short rod-shaped cells swim with the help of a handful of flagella distributed peritrichously around their cell body. When they encounter a solid surface, the cells elongate and build many more flagella, as you can see on this cell. Instead of swimming, they now use their flagella to propel themselves in groups across the surface, a motility mode known as “swarming.” This is an example of a differentiated lifecycle, which will come up again in Chapter 8.