  We consider a colony of point-like self-propelled surfactant particles
(swimmers) without direct interactions that cover a thin liquid layer on a
solid support. Although the particles predominantly swim normal to the free
film surface, their motion also has a component parallel to the film surface.
The coupled dynamics of the swimmer density and film height profile is captured
in a long-wave model allowing for diffusive and convective transport of the
swimmers (including rotational diffusion). The dynamics of the film height
profile is determined by three physical effects: the upward pushing force of
the swimmers onto the liquid-gas interface that always destabilizes the flat
film, the solutal Marangoni force due to gradients in the swimmer concentration
that always acts stabilising, and finally the rotational diffusion of the
swimmers together with the in-plance active motion that acts either stabilising
or destabilising. After reviewing and extending the analysis of the linear
stability of the flat film with uniform swimmer density, we analyse the full
nonlinear dynamic equations and show that point-like swimmers, which only
interact via long-wave deformations of the liquid film, self-organise in highly
regular (standing, travelling and modulated waves) and various irregular
patterns for swimmer density and film height.
