Non-target predatory insects can be indirectly exposed to aerial pesticide spraying and fogging to control Monochmus beetles that transmit pine wood nematode, Bursaphelenchus xylophilus. We evaluated potential lethal or sublethal effects of thiacloprid on survival and behavior of a carpenter ant species, Camponotus japonicus Mayr. Field-collected ant colonies were directly exposed to several food items, such as thiacloprid-addicted Monochmus beetles, 10% sugar watered cotton balls contaminated by thiacloprid concentrations, and 10% sugar water. Dead beetle bodies caused no apparent adverse effect through dietary exposure in general, although a few ants were died with paralysis at colony level experiment. At individual level, most ant workers were died within 10 days compared to control group. In contrast, dietary exposure of ants to thiacloprid concentrations showed significant lethal effect with paralysis and impaired walking, especially at 10 and 50 mg/L thiacloprid concentrations. Some intoxicated ants recovered within a few days in 10 and 50 mg/L thiacloprid concentrations, but intoxicated ants were generally shown to be less responsible to enemy ants with low aggressive behavior. Implications for predicting hazards of thiacloprid to beneficial arthropods in pine forests are discussed.