The Collaborative International Dictionary of English v.0.48:

Plant-eating \Plant"-eat`ing\, a.
   Eating, or subsisting on, plants; as, a plant-eating beetle.
   [1913 Webster]

WordNet (r) 3.0 (2006):

plant-eating
    adj 1: (of animals) feeding on plants [syn: plant-eating(a),
           phytophagic, phytophagous, phytophilous]