An Etymological Dictionary of the German Language/Annotated/Assel
Assel, masculine, especially Kellerassel, ‘woodlouse,’ Modern High German only; generally derived from Latin asellus, ‘little ass,’ and might have been named from its grey colour; compare Greek ὄνος, ὀνίσκος, ‘ass, woodlouse,’ Italian asello, ‘woodlouse.’ Yet the ss the Modern High German word, as well as the dialectic variant atzel, might militate against this derivation; hence a pre-Teutonic stem at, att (allied to essen?) seems to be at the base of it. Compare also Esel.