Commentary Purg X 128

While God wills that we, caterpillars that we are, become butterflies, Heaven-bound souls, we choose to be even less than those worms that are capable of that transformation, and have bent our wills to be such.  As commentators have shown, antomata is Dante's version of Aristotle's creatures born, not of other creatures, but of the putrefaction of vegetable matter, as when the sun beats down on the mud -- see De generatione animalium III.1, as cited by Benvenuto (DDP Benvenuto.Purg.X.124-129).  See also Aristotle's Historia animalium V.19, as cited by Pasquini/Quaglio (DDP Pasquini.Purg.X.128-129), where Aristotle distinguishes, as Dante does here, between worms that can turn into butterflies and those, defective, which cannot.  The meaning clearly seems to be that we are born worms, but turn ourselves into still lesser beings, formally imperfect worms, as though we had not been bred by creatures with rational souls.  Benvenuto concludes by quoting Job (but actually the Psalms [21:7 [22:6]): 'Vermis sum ego et non homo' (I am a worm, not a man).  Benvenuto may have conflated that passage with Job 25:6.]