We report evidence of a new trophic interaction in nature whereby a parasitic plant attacks multiple species of insects that manipulate plant tissue when the two co-occur on a shared primary host plant. Most plant species are attacked by a great diversity of external and internal herbivores [1]. One common herbivore guild, gall-forming insects, induce tumor-like structures of nutrient-rich plant tissue within which immature insects feed and develop [2,3]. While the gall is made of plant tissue, its growth and development are controlled by the insect and it therefore represents an extended phenotype of the gall former [4]. Typically, parasitic plants attack other plants to gain nutritional requirements by connecting directly to the vascular system of their hosts using modified root structures called haustoria[5]. Here, we document the first observation of a parasitic plant attacking the insect-induced galls of multiple gall-forming species and provide evidence that this interaction negatively affects gall former fitness.