The strange moth returned today and I was right there waiting with the camera set to shutter priority at a shutter speed of 1/350th second. That froze the motion of the wings quite nicely! From what I see on the web, it looks like it's a clearwing hummingbird moth. End of mystery! 🙂
Hi, I found your picture at Garden Voices, just to let you know we have some of those moths here in Germany too. "Humming-bird Hawk-moth" or "Macroglossum stellatarum" is it's name! Look here if you like: http://www.schmetterling-raupe.de/art/stellatarum.htm In German language it's called "Taubenschwänzchen" . It looks almost like yours! Unfortunately we have no real humming birds here Great photo btw!
Thanks for the kind words, Carol — much appreciated. 🙂 The Clearwing Hummingbird Moth pictured here is "Hemaris Thysbe", a related species.