Gigantodax is a genus of 68 species of black flies distributed along the Andes from Mexico to Tierra del Fuego in Argentina. The taxonomy of the genus was revised in 1989 by an academic paper published in the bulletin of the American Museum of Natural History. In 1997, researchers from the Universidad Nacional del Comahue in Rio Negro, Argentina collected larvae of G. marginalis and other fly species in Lanin National Park, Neuquén Province. After a close examination included chromosome mapping, they reported: