It looks like it came from some form of pest, but there are no obvious holes or material above it. It's between glass and a screen with no obvious openings or holes. None of my other windows have it. We did have the house re-insulated recently, but I don't think it looked like this. Any help identifying what's going on?
I'm geographically located in Northern NJ I'm the US in the suburbs.
Maybe carpenter ants. At one point I discovered them by a pile of sawdust like that on my coffee table.
It turned out there was enough of a roof leak to cause some rot despite no visible leak symptoms, the ants were following that, and happened to discard the sawdust out a tiny hole in the ceiling above my coffee table. It sucked because that was the signal to replace the roof