 and it's not bot mulch, what do you think that is? In most cases, it's probably slugs. And one way to tell is put a board out in the area. You moisten the board underneath, put it down in the evening, and the next morning. Slugs love during the day to be in moist places, and oftentimes you'll find them under that board, and then, of course, you can get rid of the slugs.