Austrosimulium is a genus of about 30 species of black flies that are distributed in Australia and New Zealand. There are 2 subgenera: Austrosimulium whose species are principally from New Zealand, and Novaustrosimulium which are exclusively Australian. Austrosimulium is a sister genus to the monospecific Paraustrosimulium of South America.

Some species are known to spread the protozoan blood parasite Leucocytozoon tawaki in penguins.

In New Zealand, where they are known as sandflies or namu (in Māori from Proto-Austronesian *ñamuk "mosquito", compare with Malay: nyamuk), three species – A. australense, A. tillyardianum and A. ungulatum – bite humans.

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