Lygus bugs (Heteroptera: Miridae) are important pests of several crop plants. For the development of an efficient monitoring and forecasting system for Lygus densities, low catches of bugs with yellow sticky traps have been a problem. We determined the spectral reflectance of yellow and blue traps and compared their catches of Lygus spp. during five consecutive growing seasons in carrot fields, with additional data collected from other crop plants. Blue sticky traps caught significantly more omnivorous Lygus rugulipennis (Popp.) than yellow sticky traps in carrot fields. Lygus kalmi (L.) that is a typical species in carrot fields, was equally caught by yellow and blue traps. Our results suggest that blue sticky traps are a convenient method for monitoring of L. rugulipennis especially during the seedling stage of cultivated carrot plants when sweep netting cannot be used. Factors affecting the efficiency of blue sticky traps to capture omnivorous bugs and thrips are discussed.