Eupatorium adenophorum is a noxious invasive weed that is distributed throughout subtropical areas worldwide. Enemy release may be at least one of the reasons underlying its success as an invader. In this study, we observed damage to the epidermis, cortex, phloem, cambium, and xylem tissues of roots and stems around the root collar of E. adenophorum growing in an experimental field in Yunnan Province, southwest China. The damage was caused by Dorylus orientalis, a polyphagous ant feeding on the weed and resulted in the death of the plants by interrupting nutrient exchange between shoots and roots. This ant showed selectivity for the invader to some extent. The finding of D. orientalis and other native enemies indicate that E. adenophorum may gradually naturalize in introduced landscapes. In addition, this ant may have potential for use as a biocontrol agent against the invader.