  Black holes have turned into cosmic laboratories to search for ultra-light
scalars by virtue of the superradiant instability. In this paper we present a
detailed study of the impact of the superradiant evolution on the black hole
shadow and investigate the exciting possibility to explore it with future
observations of Very Long Baseline Interferometry. We simulated the
superradiant evolution numerically, in the adiabatic regime, and derived
analytic approximations modelling the process. Driven by superradiance, we
evolve the black hole shadow diameter and (i) find that it can change by a few
$\mu$as, just below the current resolution of the Event Horizon Telescope,
albeit on timescales that are longer than realistic observation times; (ii)
show that the shadow diameter can either shrink or grow; and (iii) explore in
detail how the shadow's end state is determined by the initial parameters and
coupling.
