The eggs and all four larval instars of Austroconops mcmillani Wirth and Lee and A. annettae Borkent, new species, are described. The pupa of A. mcmillani is also described. Life cycles and details of behavior of each life stage are reported, including feeding by the aquatic larvae on microscopic organisms in very wet soil/detritus, larval locomotion, female adult biting habits on humans and kangaroos, and male adult swarming. Austroconops annettae Borkent, new species, is attributed to the first author.

Cladistic analysis shows that the two extant Austroconops Wirth and Lee species are sister species. Increasingly older fossil species of Austroconops represent increasingly earlier lineages. Among extant lineages, Austroconops is the sister group of Leptoconops Skuse, and together they form the sister group of all other Ceratopogonidae. Dasyhelea Kieffer is the sister group of Forcipomyia Meigen + Atrichopogon Kieffer, and together they form the sister group of the Ceratopogoninae. Forcipomyia has no synapomorphies and may be paraphyletic in relation to Atrichopogon. Austroconops is morphologically conservative (possesses many plesiomorphic features) in each life stage and this allows for interpretation of a number of features within Ceratopogonidae and other Culicomorpha. A new interpretation of Cretaceous fossil lineages shows that Austroconops, Leptoconops, Minyohelea Borkent, Jordanoconops Szadziewksi, Archiaustroconops Szadziewksi, and Fossileptoconops Szadziewksi form a monophyletic group. Within this assemblage Leptoconops and Minyohelea are sister groups and Austroconops and Jordanoconops are monophyletic (Austroconops is possibly paraphyletic in relation to Jordanoconops). All are considered to be members of Leptoconopinae Noè and the subfamily Austroconopinae Borkent, Wirth and Dyce is a new synonym of Leptoconopinae.

Extant and fossil distributional records suggest that Austroconops was displaced from its previously broad distribution by the emergence of Culicoides Latreille. Larval feeding on microorganisms is plesiotypic within the Ceratopogonidae and Chironomoidea, and living in small aquatic habitats is plesiotypic within each family of the Culicomorpha. Outgroup comparisons further suggest that diurnal feeding by adult females is plesiotypic within the Ceratopogonidae and Chironomoidea.