What insect makes tiny nests on painted wooden basement wall inside house in well-lighted area? The nests look like gray spattered concrete, less than 1 cm in size. The irregularly shaped nests are different sizes scattered about. One protrudes out a bit. Near the nests I found a tiny black fly-like insect clinging to wall. But I also found a spider. I have searched on internet, but cannot find any photo like these spatters.