The western tarnished plant bug, Lygus hesperus Knight, overwinters in an adult diapause. However, the ecological implications of diapause to L. hesperus population survival are poorly understood. Enhanced understanding of L. hesperus overwintering ecology might reveal opportunities to develop ecologically-based management tactics. One factor limiting efforts to understand the dynamics of overwintering is lack of a non-destructive method to distinguish diapause. We evaluated a suite of external characters for utility in distinguishing diapausing from non-diapausing L. hesperus. Abdomen coloration of female L. hesperus was a highly reliable indicator of diapause status. During these studies, a single female (0.6%) was misclassified using the abdomen color criterion. For male L. hesperus, corrected abdomen length (abdomen length / head capsule width) was used to predict diapause status with ≈84% accuracy. Both criteria provided improved accuracy compared with earlier reports, in part because their application was limited to adults of a specific age (10 d) and reared at a specific temperature (26.7°C). Application of these criteria to individuals that were subsequently starved allowed us to unambiguously distinguish the survival functions of diapausing and non-diapausing males and females. Although neither criterion (abdomen color for females, corrected abdomen length for males) was error-free, both offer sufficient accuracy to justify their use in studies of the ecology, physiology, or molecular biology of L. hesperus diapause. These criteria provide the ability to non-destructively distinguish the diapause status of adult L. hesperus with reasonable accuracy, and should enhance efforts to better understand diapause and overwintering ecology in this important pest species.