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.
This the pollen of the sawdust tree! Quercus alunima. It thrives in moderate, humid climates. It releases pollen that, when aggregated, looks like piles of sawdust. This used to confuse early settlers when they first colonized America. The puritans used to call it 'the devil's sawdust' since it appeared out of nowhere like magic. But the tree is perhaps most famous for not actually existing because I just made all that up.