This is a coincidence...I just had my bug guy check my place yesterday for termites & I have a spot like pic #2 in my coal bin area. It's a dirt floor, no insulation & it's "growing" where the floor joists & concrete wall meet. He told me the area needed to be treated with (I believe) borax & I need a vapor barrier on the floor & Insulation up top.
Does this sound right? I agree I need the insulation, since above that space is my office & my pantry & those 2 rooms are really cold in the winter time. I figure this might be something I can address on my own...rather than pay them. The estimate was $700. !