Plant galls are induced by physicochemical interactions between plants and gall-inducing organisms, such as insects, mites, nematodes, fungi, bacteria and viruses. Organisms that are unable to create galls on plants, but feed on gall tissues induced by other species, are referred to as gall-attackers (gall-feeders) and include various insect orders (Thysanoptera, Hemiptera, Lepidoptera, Coleoptera, Diptera, and Hymenoptera). Gall-attacking weevils (Coleoptera) and moths (Lepidoptera) may have acquired their gall-feeding habits independently (i.e. cecidophages), whereas other gall-attacking insects, such as inquiline gall wasps (Hymenoptera) and gall midges (Diptera) may have evolved these habits from gall-inducing ancestors (i.e., inquilines). Most species of gall-attacking weevils feed only on galls (obligate cecidophages), while most gall-attacking moths feed on galls and also on ungalled or normal plant tissues (facultative cecidophages). Weevils may have acquired their gall-attacking habits independently from other types of feeding habits, such as leaf mining, seed-feeding, and bud-feeding, while moths may have acquired them from leaf-chewing and wood-boring. Studies on the effects of gall-attacking weevils on gall-inducing arthropods report a higher proportion of lethal effects than studies on effects from gall-attacking moths. Weevil larvae rarely move around food resources because they have no legs, while moth larvae can actively move among food resources using their prolegs. This difference in mobility between weevils and moth larva may be related to their differential gall-attacking behaviors and effects on gall-inducers. Cecidophages provide a model system for investigating the evolution of feeding habits and the ecology of species interactions.