  How particles are deposited at the edge of evaporating droplets, i.e. the
{\em coffee ring} effect, plays a crucial role in phenomena as diverse as
thin-film deposition, self-assembly, and biofilm formation. Recently,
microorganisms have been shown to passively exploit and alter these deposition
dynamics to increase their survival chances under harshening conditions. Here,
we show that, as the droplet evaporation rate slows down, bacterial mobility
starts playing a major role in determining the growth dynamics of the edge of
drying droplets. Such motility-induced dynamics can influence several
biophysical phenomena, from the formation of biofilms to the spreading of
pathogens in humid environments and on surfaces subject to periodic drying.
Analogous dynamics in other active matter systems can be exploited for
technological applications in printing, coating, and self-assembly, where the
standard coffee-ring effect is often a nuisance.
