Hummingbird moth (Hemaris thysbe) drinking nectar from a wild bergamot flower in my garden two days ago (Warren County, NJ).
This insect must have evolved as a "hummingbird mimic"...but why? Even the eye looks like a vertebrate eye, with a dark "pupil" in a brown "iris" (click on bottom picture). The white belly and dark back (known as "bicolored") is a common coloration among birds and other vertebrates. I think the clear patch in the wings makes them look more like the blur of a hummingbird wings. The whole package must be meant to give pause to potential bird-predatator, which presumably couldn't (or at least wouldn't) dine on a fellow bird.