Hers a new one I haven't heard about yet- my insert is full of flies, WTH! I just set out 20 rat traps around my stacks, and now this. I keep hearing all the buzzing of a fly, so I track the sound down to the insert area and then I see them. Several flies crawling on the inside of the glass. They must have come down the flue, but why. I wonder what attracts them, creosote? I have a new flue, just last seasons worth of use, I haven't swept it yet.