In Australia, eriococcid scale insects are the dominant gall-inducers. In contrast to work that has been done on cecidomyiids or cynipids in the northern hemisphere, a transition series from simple to complex galls has never been demonstrated for eriococcids. Most eriococcid galls are complex, often sexually dimorphic, enclosing structures. The genus Lachnodius Maskell is unusual in being comprised of some species that are free living, and others that induce either simple pit-galls, or more complex enclosing-galls. Relationships among Lachnodius species and representatives of the closely related genera Sphaerococcopsis Cockerell and Opisthoscelis Schrader were inferred by parsimony analysis of morphological characters of the adult females and first-instar nymphs. Gall-traits were mapped onto the resulting phylogenetic tree. Lachnodius is paraphyletic with respect to Sphaerococcopsis and Opisthoscelis. Gall-induction has arisen once within the group, followed by several transitions from pit-shaped structures to enclosing ones.