I don't consider flies to be pests, since I like all animals and plants, and there aren't too many flies here. But since many of you consider flies to be pests, you probably know how to kill them or get rid of them. I recently planted three arborvitae trees and two american hazelnuts. They are less than two feet tall. Two of the arborvitaes are dying. On the third one, I saw at least 8 flies. There were also at least five on each of the two hazelnuts. They were not eating from any of those plants, just sitting there. After about two days, they were all dead. They were still on the plants, even the ones that were upside down, but when I touched them, they didn't even twitch a leg. Does anyone know how they died, or if they just land on a plant when they are old (for flies) and just wait until they die?