We report 21 thelastomatoid species parasitizing 31 described and 5 undescribed geoscapheine and panesthiine cockroaches, representing all but 1 of the known species of these subfamilies in Australia. The nematodes have 3 distinct patterns of host distribution: dominant, moderate and rare. The 4 dominant species, Cordonicola gibsoni, Leidynemella fusiformis, Travassosinema jaidenae and Aoruroides queenslandensis, are highly prevalent, found in nearly all host species examined, and broadly distributed. The 8 moderate species have lower prevalences but are still widely distributed. Many of these species are more common in one host subfamily than the other. The remaining 9 rare species have highly restricted host and geographical distributions. Six of the 21 species are exclusive to geoscapheines, 5 to panesthiines and 10 are shared. These patterns suggest that most of the reported thelastomatoid species are generalists rather than specialists, that host-specificity within this group is low and that co-evolutionary speciation has had little, if any, impact on structuring the thelastomatoid fauna of Australian burrowing cockroaches. In a broader context, this study provides the first comprehensive examination of the role of coevolutionary speciation and host specificity in regulating the distribution of pinworms in arthropods.