Inside my house on a window sill there is a little mound (size of a dime) of what looks like finely ground pepper. I cleared it away and in just a few hours the little mound re-appeared. What could it be?
By nan rae
I think it could be carpenter ants. Do you have a tree anywhere near your house that is dead or a decaying bush? That is where carpenter ants come from. I had them once and sprayed all along the perimeter of my basement and they left but someone told me they come from a decaying tree. We had an apple tree that had died and we cut it down but the stump was still in the ground so that is where mine came from.
That is called black mold and is the kind you don't want to breed. Bleach it and keep the area dry. It grows real fast and can become a problem. It breeds in moisture.
Assuming you mean a loose material piling up; if so probably ants. Go straight up from the pile and see if you see a small hole or opening in the wall, if so ants are using an area as a dumping ground, causing the debris pile to show up.
I was just about to post that it sounded like carpenter ants or carpenter bees. I had the same thing on my front porch and watched and they ewre puffing it out of a hole I would have never noticed.