  Motile bacteria are known to accumulate at surfaces, eventually leading to
changes in bacterial motility and bio-film formation. We use a novel
two-colour, three-dimensional Lagrangian tracking technique, to follow
simultaneously the body and the flagella of a wild-type ${\it
Escherichia~coli}$. We observe long surface residence times and surface escape
corresponding mostly to immediately antecedent tumbling. A motility model
accounting for a large behavioural variability in run-time duration, reproduces
all experimental findings and gives new insights into surface trapping
efficiency.
