(Columbia desert parsley is an interesting story in itself. It’s the only member of its family that I know of with pink flowers – and pink pollen. It’s quite common along that stretch of the river, but is found nowhere else in the world.)
It’s an asilid fly. A robber fly. An assassin fly. A nuisance (if you’re looking for bees.) On the off chance that last point wasn’t clear enough, it’s snacking on Ceratina, a small carpenter bee. My immediate reaction was, where did you find that? It’s a terrible burden, being shown up by an insect. I never did see a live one that day.
I have spent days in prairie where the seed pods stood out of the grass, maybe a foot above the other blades, and on every one there was a robber fly, watching for prey. Those are boring days, if you’re there to photograph other insects. Robber flies may not match the dragonflies for sheer killing efficiency, but they are entirely capable of making up for it with numbers.
Actually, I may be selling them short. This one was alone, and it still managed to kill every bee in sight. (OK, it was just the one.)
I’m probably not adequately conveying the existential despair that goes with standing under grey skies on a wind-blasted slope above the Columbia River, working your hands to restore enough blood flow to focus the macro lens, and watching a fly eat your principal subject.
On the other hand, it’s a good looking fly.
(Note on ID: I’m not good with Asilidae, and this isn’t a particularly useful angle. There is a genus, Mallophora, that is famous for eating bees, but I’m pretty sure this isn’t one of them. If I had to guess – which I don’t, but will anyway – I’d say it’s probably Efferia. The head and body shape are about right, and there are several species in the area.)