Hey everybody!
I recently hung up my pencil work at a cafe. It took a long time to properly assemble everything -- specifically, I've got glass, mat, drawing, foam, and then it's all sealed with screws around the picture frame.

It was up for a few days and all of a sudden I found little teeeeany bugs on my black mat. These bugs are really gross looking, almost transparent but stick out as white on my black mat. Any reason for this happening? Now I've got about 10 of these buggers in one of my pieces, and 5 or so in another, and like, 2 in the last.

I haven't shown my pieces much in the past framed with glass and mats and all. What in the world is this? Why's it happening?

Thanks everybody!