Abstract The bug Cynodonmiris corpoicanus inhabit the Cundiboyacense High Plateau in Colombia feeding on grasses (Poaceae). The authors carry out their life cycle in greenhouse and characterize the damage on oat (Avena sativa) leaves. The duration egg - adult last 49.3 days and undergo five nymphal stages. The morphometric study was conducted by principal component analysis (PCA) and 2.03 PAST software. This method let to determine measures for nymphal stages separation, furthermore we consider coloration, morphology and morphometric description. A key for nymphal stages determination was developed by morphometric and morphology diagnostic characters. Also, we include illustrations of the C. corpoicanus nymphal stages.