bobdog, to be honest I don't have a very clear picture of your system(s), but I'll make a few general points.
Cutting food scraps isn't at all necessary for the BSF. Maybe you're doing this because you're sorting/screening the castings later? I don't know much about traditional composting so maybe that's why I don't understand some of your procedures.
For a filter or pre-filter you might try using coconut fiber (coir). It's biodegradable, cheap, and seems to be effective. I now recommend a one inch coir liner for the bottom of BioPods to keep the drain and filter medium from clogging. I have two pages on my blog that show coir being used. One is the "tips and tweaks" page for setting up a BioPod, and the other is part of a DIY bucket BSF bio-composter (repeat that rapidly six times) I'm working with now. I used plastic pot scrubbers as a final filter medium in a modification to my BioPod drain which is also on the "tweaks" page.
The tighter lid you mention might cause more problems at some point than it solves. BSF colonies usually need a lot of ventilation in hot weather. Maybe it works for your set up, but keeping out other fly species is automatic if you have a dense and balanced BSF colony working.
The adults you see at your bin are females looking for egg laying sites. They are in no way territorial. The only territorial behavior observed in BSF is between adult males and it's not at all violent.
Stirring the muck in your bin is also something that would be unnecessary with a balanced BSF colony. In a thriving colony aeration is provided by the churning action of the grubs.
I can't imagine BSF developing on the stuff vacuumed from your floor. Hair and plant fibers will be ignored and a few crumbs of food wouldn't last two minutes in normal BSF colony.
I'm not trying to discourage you in any way. I think if you keep studying and experimenting with BSF you'll figure out exactly how you want to use them and the best way to do it. You might want to try out my DIY composter. I would do like to hear what you think about it.
I'm looking forward (with some trepidation ) to updates on your progress.
) to updates on your progress.
