Seen grazing on... algae? on the surface of our plastic compost bid. It's head was bobbing and it was definitely gnawing on something, but I couldn't make out what. That said, I have seen other bark lice of other species on our compost bin, so it could be algae or pollen on it's surface, or residues left from the contents splattering about or insects walking on the filth inside then clambering on the outside of the compost bin. Who knows.