When I first saw this concentration of syrphids from a distance, I was intrigued by their numbers and stealthily approached so as not to scare them off. However, when I drew within close range without any response, I knew something was amiss. I discovered they were all dead and firmly attached the plant. As I proceeded to investigate, I noticed hundreds of them in the top-most twigs of this shrub (Tetradymia axillaris var. longispina in the Asteraceae) and in neighboring shrubs of the same species. Viewing them with a hand-lens, it looked as if they had succumbed to a fungus. Later I read about flies falling prey to entomophagous fungi, which is what I presume occurred here. The fungus seems to have managed, through natural selection, to somehow compel its perishing victims to seek out and cling to high, exposed twigs, which presumably aids in dispersal of the spores.

My best guess at the syrphid genus here is Eupeodes (perhaps E. volucris?).