One of the light fixtures in the ceiling of my TT has filled with styrofoam powder. When I take down the fixture, the insulation above it is powdered. It's as if something is living up there and chew...
I periodically will clean the ceiling lights of stuff that falls in there. No evidence of creatures. I have styrofoam in the roof. I have had carpenter ants make homes in the foam sheathing on my house. When I built houses, we would leave all manner of detritus in the walls, messages, too. No one would know until the wall was taken apart, maybe never.