A couple of months ago I found a lot of small yellow solid dots on the shelves of the bookcase in my bedroom. As it was an old piece of furniture, so I took the chance to buy a new one. I carefully cleaned the area before installing the new bookcase and I thought I had solved the problem.
Unfortunately a few days ago I noticed the same yellow dots on the bookcase of the living room. This bookcase is way bigger than the other and custom made, therefore changing it is not an option. I did some brief research but I could not find out what kind of mold it is and how to permanently remove it (possibly because it is not a mold, maybe the excrement of some kind of insects or even something else… I don't know!).
I attach below an image of the problem: the radius of those yellow dots is about 1 millimeter, they are in relief respect to the surface of the shelf and they are somehow glued to it, but they can be removed scratching the surface (finger nails are enough).
P.S.: In addition to wooden surfaces they seem to like sticking on my books too. If removed most of the time they leave a yellowish ring on the paper.
EDIT: I should mention that I live in the city center of a northern Italian city and it's nearly winter here.
Best Answer
It looks like excrement from an insect, quite possibly one that has been eating pollen (which gives a dark yellow colour). I suspect some sort of fly. The photo show two neatly overlapping spots, so unlikely to be fungi.