Badisis is a stilt-legged fly genus with only one known species, Badisis ambulans. This is a wingless, haltere-less fly with an ant-like appearance. It is only found in the Southwest Australian bioregion of Western Australia. Dependent on the rare Albany Pitcher Plant (Cephalotus follicularis) for its development, this fly is also a rare species. Despite its many apomorphic features, the details of its morphology suggest a close relationship to the diverse genus Metopochetus, which is also in the tribe Metopochetini. The fossil stilt-legged fly Electrobata tertiaria from Baltic amber of the Paleogene also shows some similarities; it may be a very basal member of the Metopochetini, close to the divergence between these and the Eurybatinae. Description Apart from its lack of wings and halteres, B. ambulans has a less unusual habitus than other members of the Micropezidae. Its body is stockier, with a petiolate abdomen (like in ants and other Apocrita), its middle and hind legs are less elongated, and its forelegs are less shortened than in its relatives. At a casual glance, it is easier to confuse with an ant than with other micropezid flies. The two sexes are almost identical; they can be told apart essentially just by microscopic study of the tip of the abdomen. The larva is adapted to its strange habitat, the pitchers of the Albany Pitcher Plant. In third-instar larvae (and likely in others too), the slits of the posterior spiracle are entirely closed. Head The compound eyes are as large like in Metopochetus, an unusual feature among wingless Diptera, many of which lack them altogether. The third antennal segment of Badisis is elongate-oval. There are usually three bristles (setae) on each side of the "forehead". Rare among stilt-legged flies but also found in Metopochetus, there is a knob below the postvertical bristles. The prelabrum is large but not markedly projected forward at the lower margin. Thorax The scutellum is distinctly visible but rather small. Like in most other Eurybatinae, there is no groove connecting the mesoscutal transverse sutures across the centerline of the mesothorax. The metathorax has a dorsal sclerite shaped like a saddle. Abdomen The petiole is formed by the first two segments of the abdomen, the first of which has a slight bulge on the tergite. In the male the postabdomen is highly characteristic, the sternite of the 5th postabdominal segment is shallow divided into 2 lobes, each of which bears