My wife came upon this poplar hawk moth (Laothoe populi) when she was gardening. It was a species we had never seen before, and after researching it we wondered why: it is, by all accounts, reasonably common. However, it is very well camouflaged and therein, I think, lies the reason we hadn't encountered it before. There are several hawk moths and this one, as its name suggests, feeds on poplars (white, black and lombardy) as well as sallows and willows. All of those can be found in the areas where we live.
photo © T. Boughen Camera: Olympus OMD E-M10 2018