Dark Brown dust on my floor

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?
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probably carpenter ants, worth getting rid of.
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When you open the door om your cottage and it collapses into a pile of dust, then you will not find one termite left there. They will have moved on to your nearest neighbors place..I seen this happen one time in service. They had stored oak desk in a second storied building for about three years. When they went to move them out, mibd you they looked perfect except for dust, When they were touched they collapsed in a pile of dust.
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