If you've ever seen one of these flies, you'll know how the word ethereal applies to its habit.
This specimen is only about 10mm - much smaller than the other specimen pictured here, which is about 15mm.

Conopids are most frequently found at flowers, feeding on nectar with their long proboscis. Flies of the family Conopidae are distributed in all the zoogeographic regions except for the poles and many of the Pacific islands. About 800 species are described worldwide, approximately 67 of which are found in North America. The majority of conopids are black and yellow, or black and white, and often strikingly resemble wasps, bees, or flies of the family Syrphidae, themselves notable bee mimics. The larvae of all conopids are internal parasites, most of aculeate (stinging) Hymenoptera. Adults are said to alight and deposit eggs on their flying hosts.