Sometimes misidentified as the "hummingbird moth”. The Snowberry Clearwing Moth (Hemaris diffinis) seen out of the corner of you eye is decidedly Hummingbird-like in size and disportment. Adult hummingbird moths feed on nectar from a variety of flowers, but their larvae need more specific food plants, such as several species of honeysuckle, dogbane, or some members of the rose family such as hawthorn, cherries, and plums.
You would think something like this would be rare but they can be seen most summers on hot days such as we have enjoyed (I use that word advisedly) earlier this week.
Worldwide there are actually approaching 1000 species of Clearwings but only four (I think) in North America. The Snowberry is certainly the one we see most regularly where I live. They are day-flying insects and can be effective, and sometimes important, pollinators.