I'm personally against using flies as a staple. I recently bought some fly pupae and love them They just seem to small for a staple; you would need lots and lots to make him/her full. I stick to crickets as a staple but always have some flies in their ready to hatch. I add new pupae every 3 days or so so he has enough time to eat them all. As of now, he seems to like both equally as much. I would however consider changing staples to roaches; they are big enough and easy to care for.