Milichiella rugosistyla was collected in bat caves.
Differs from congeners in the combination of shiny frons, subshiny mesonotum, yellow halter, and silvery male T2-5.
Male coloration and vestiture: frons shiny black, ocellar triangle and orbital plates shiny black, lunule brown, basoflagellomere dorsobasally brown, rest orange, face brown microtomentose, lateral margins yellowish silvery, palpus yellow brown; thorax with mesonotum subshiny black, more shiny on posterior half, scutellum shiny, pleura brown microtomentose except for shiny spot on an- and katepisternum, wing hyaline to whitish, veins hyaline to light brown, brown spot at tip of vein R1 present, calypter white, halter yellow, legs black; abdomen with T2-5 silvery microtomentose. Female coloration and vestiture: lunule, basoflagellomere and palpus more yellow than in male, halter yellow, basitarsi yellowish, abdomen with T2-4 slightly brown microtomentose dorsally, shiny laterally, T5 subshiny.
Morphology. Head: frons with ? (female: 2) orbital and ? frontal setae, anterior frontal seta ?. In males frons 1.9x as wide at posterior margin than at base of antenna, arista about 4.3x as long as basoflagellomere wide, pubescence on arista very short, posterior eye margin with wide notch (8oc) and narrow emargination (2oc).
Thorax: 2 dc, 1 prsc, ? pprn, 1 prs, ? keps setae, posterior prsc about as long as posterior dc, seta between posterior prsc and posterior dc absent. Wing with vein R4+5 and M1 strongly converging (6.0), and ultimate section of vein M1 1.8x as long as penultimate section. Fore femur normal setulose, tibial organ absent.
Male abdomen: posteromedial triangular projection of T1 into T2 present. Tergal chaetotaxy: T2 anterolateral corner with 2-3 lines of setae, T2-5 posterior margin with 1-2 rows of setulae. S5 1.1x as long as wide, 1.8x as long and 1.7x as wide as S4, posterior margin indented, strongly setulose with short setae. Male genitalia with apical seta on cercus as long as longest epandrial seta and 0 setae on subepandrial plate, surstylus 0.5x as long as epandrium high, dilated apically (1.4x), straight, 2.8x as long as wide, structure of lateral surface slightly wrinkled, medial surface without setulae, longer sensilla along margin.
Special characters: M1 bending to R4+5 quite sharply near wing margin.
Body length: ? mm; wing length: 3.2 mm.