Lumpus, I've fed my larvae fresh whole fish on a hot summer day without any problem from house flies or blow flies. I recently ran into trouble adding fish because they were partially decomposed when I added them. My small colony managed to process the fish quickly but the odor was a powerful attractant for pest flies. It made my unit unpleasant for almost 2 weeks. I won't do that again. If you want to give your larvae a high protein diet I recommend using fish pellets or some type of animal feed. That type of food doesn't have a strong odor and shouldn't attract pest flies. Be aware that if you feed them only a dry mixture you will need to add water. Also, a little dry feed goes a long way and it's easy to over feed them.
EDIT: When I fed my colony freshly dead fish there was almost no odor noticable outside the container, even on a hot day. I saw 2 house flies in the vacinity of the colony in the hourly trips I made to the container that day. The chances are pretty good you will see 2 house flies anywhere. on any given day.
rmedgar, sometimes you will get a large percentage of large gray larvae exiting the unit. These larvae will transition to the black and final larval stage soon after they migrate out.
