Can anybody tell me what this is

[wednesday2345]

This keeps appearing on the same spot of floor in my home. I clean it and then it reappears over night.

It looks like soot. Birds nesting in your chimney maybe ?

What's behind the wall?

Mould

The other side of the wall is the living room so it is an internal wall. Is it possible to get mould on an internal wall?

I should probably add that there is no damp/mild on the wall itself, it's just that part of the floor that it appears from.

What's the internal wall made of?

Is the flooring on the ground floor, could this be dirt coming up from the ground?

@dudsville no, we are in a flat which is on the first floor so it can't be coming from the ground. Not 100% sure what the wall is made from but it isn't a new build property.

We had similar with carpenter ants. Have you seen any ants?

Any noises that might be a creature in the wall ? A mouse ?

Is it loose like dust or do you have to get an old tooth rush and scrub it?

It looks like the dust ants push out from their nests.

It's ants 100%
I have the same outside my front window.

One of my neighbours had pest control guy out for something else, and I asked him.

Also came to say ants. I've had this before. Put some ant powder down and keep hoovering out every other day or so.

Yes ants. We had them travel up our cavity walls and appear upstairs in the bathroom. They also travelled through the floorboards and behind skirting. We had to find where they first came into the house (via the backdoor wood frame) and put poison down, which they eventually found and took back to the nest. They are buggers!