i agree that the moral problem that poses is dwarfed by that of the suffering or factory animals. But you can well ask, where are the boundaries? I mentioned fish in what i said, for i do believe that fish are also capable of feeling pain. When we get beyond vertebrates, it does get more difficult. That you mentiond a fly once we talk about insects, then i think it's really hard to know whether insects are conscious beings. It's certainly possible that they are, but their behaviour, in some ways, is more pre programmed, not always.