Eucalyptus insect communities in Australia are largely composed of gall inducers, mainly the chalcid families Eulophidae and Pteromalidae. The Eucalyptus gall wasps display infrequent occurrences in their native area in contrast to the serious damage inflicted in their invasive range, mainly by the multivoltine species among the 14 discussed invasive gallers. This situation revealed the primeval susceptibility of major Eucalyptus host tree species and suggests a top-down effect of parasitoids on these gall wasps in their native area. Freedom from their natural enemies allowed the rapid population buildup of these gallers. Fortuitous natural enemies do not play a significant role in restraining the negative effect of the gallers in invaded areas. The serious damage inflicted by these gallers has made the introduction of their natural enemies an urgent issue. The significant parasitoid species of invasive gall wasps belong to three families Eulophidae, Megastigmidae, and to a much lesser extent—Mymaridae. Among the 21 defined parasitoid species of the invasive gall wasps 17 are idiobiont ectoparasitoids and 18 are biparental. There is no evidence of inquilinous wasp species of any Eucalyptus gall wasp community. There are indications for a narrowly specialized development of the wasps on conspecific gallers, which makes these natural enemies suitable candidates for classical biological control. Invasion of other Eucalyptus gallers from these groups is expected; a promising solution are their parasitoids found in similar climatic areas in Australia.