In my garden this afternoon, a constant blur of motion, nectaring on a Preston Lilac (a later flowering lilac). There are three species in this area that all look somewhat similar, and all show the same behaviour, that is, nectaring at flowers in daytime, darting from blossom to blossom like a hummingbird. The other two species are:

Hummingbird moth (AKA Hummingbird Clearwing Moth), Hemaris Thysbe, by far the most common one.

Snowberry Clearwing moth, Hemaris diffinis

All are considered common, but this one I rarely see.