I owned my cottage for 10 years. About 6 years ago dark brown dust started appearing on the floor in one spot. It started in late Spring and ended when it got really hot.
I called an exterminator in. He said it was some sort of bug (I don't rememeber what) eating damaged wood; the dark brown dust was his waste. There was no point to doing anything about it because they only ate damaged wood, which didn't add any strength to the ceiling anyhow, and if he killed them, they would just reinfest in short order. The cottage had a new roof when I bought it, but there were signs of old water damage; so I presume there is some dry rotted wood up there. I just hope they added wood when they put the new roof on, but that is besides the point of this post.
I figured the problem would end when they ate up all the wood, but it is still going on after 6 years.
Does the exterminator's answer seem right. Any suggestions?