Pontania galls are miniature ecosystems containing two biologically different complexes of natural enemies; parasitic inquilines and parasitoids. Biology and quantitative importance of the parasitic inquilines are reviewed, structure and interactions of the insect complexes discussed, with reference to the various mechanisms which govern the interspecific competition and enable the coexistence in the same host population. 5 species of obligatory parasitic inquilines develop in Pontania galls: the weevils Curculio crux FABR., C. salicivorus PAYK. and Apion minimum HBST. (Curculionidae), the tephritid Euphranta (Staurella) toxoneura (LOEW) and the chalcid wasp Eurytoma aciculata RATZ. (Eurytomidae). The adults of the Curculio species and perhaps Apion minimum, too, feed upon Pontania eggs before depositing their eggs into the galls. Sometimes Pontania eggs survive, but then the larvae of the weevils eliminate the host larvae. Eurytoma aciculata deposits its eggs only after the inhabitant has been stung and killed. Its first-instar larva usually feeds a little on the host larva and then starts gnawing the tender tissues of the gall. Euphranta toxoneura shows a very surprising biology. The female deposits its eggs into galls inhibited by first- or second-instar host larvae, which at first remain undisturbed. But the hatched Eurphranta larva immediately kills the host larva and usually feeds upon it, before feeding the gall tissue. These parasitic inquilines are partly entomophagous and therefore sbd except Eurytoma sbd remarkable outsiders among their biological quite uniform relatives. That partial entomophagy as a prerequisite for the successful establishment within the Pontania galls is discussed. Sometimes larvae of optional parasitic inquilines develop in the Pontania galls: the lepidoperts Hydriomena ruberata FREY. (Geometridae), Gypsonoma dealbana FROL. and Epinotia (Steganoptycha subocellana) DONOVAN (Tortricidae), often fatal to the host. 41 hymenopterous parasitoids have been reared from Pontania galls: 13 Ichneumonidae, 11 Braconidae, 17 Chalcidoidea. The parasite complex consists of more or less specialized species, which in part attack both Pontania larvae and parasitic inquilines. In many localities not parasitoids but parasitic inquilines are the major mortality factors of Pontania.