A large sarcophagan? fly and several smaller flies were very active near an ant colony entrance at the base of a young Populus species tree which had numerous aphid colonies on the leaves and stems. The large fly would land near the entrance and proceed to almost hop around for a while, then depart only to return soon after. I could not tell if the fly was feeding on the honeydew droppings from the aphids and being disturbed by the tiny ants who's hole it was near, or if the fly was after the ants themselves for some reason.