Wow! Nectaring on common milkweed, this moth is just a little bigger than a Western Honeybee.
Have you ever seen one? I never had until Friday.
You might know them from your zucchinis. The caterpillars of Melitta curcurbitae love to eat summer and winter squashes, but if this is your reward, perhaps a little homage is in order?
Note the clear hind wings. There are several other clearwing borers in the family Sesiidae. They’re diurnal bee/wasp mimics.
Also found flying during the day are the two clearwing sphinx moths in the family Sphingidae: Hummingbird Clearwing and the Snowberry Clearwing.
Backyard and Beyond 
Gorgeous bug! Hope to see one some day. What does the caterpillar look like?
Very grubby-looking, as befits something that spends most of its time eating inside a stem: https://extension.umn.edu/yard-and-garden-insects/squash-vine-borers