The wolf and the lamb will feed together, and the lion will eat straw like the ox, and dust will be the serpent's food. They will neither harm nor destroy on all my holy mountain," says the LORD.
So if the lion eating straw is literal, then the serpent eating dust must be literal as well.
It couldn't possibly be symbolic could it? I mean with all those lamb of god, Satan being a roaring lion, Satan being a serpent, being cursed to eat dust all the days of his life, etc. references...