Very likely that's what they are then. I went mental when I first found them and poured h202 in the little trays but they shouldn't cause a problem.
Its because you have trays so that area and bottom of pot will be moister for longer which is what they like.
If you want to reduce the numbers (not that I would be ) you can put a little baking rack over your trays under your pots so air gets between the two.