Your word for today is graminivorous, which is an adjective meaning feeding on grass. For an example of its use, take this definition of abdomen from Ambrose Bierce’s The Devil’s Dictionary:
ABDOMEN, n. — The temple of the god Stomach, in whose worship, with sacrificial rights, all true men engage. From women this ancient faith commands but a stammering assent. They sometimes minister at the altar in a half-hearted and ineffective way, but true reverence for the one deity that men really adore they know not. If woman had a free hand in the world’s marketing the race would become graminivorous.