Milichiella arcuata has been collected at light, in Malaise and carrion traps, in Opuntia fields, in damp secondary growth in Acer-Betula woods, on carrion, at windows, on charred trunks, egg plants, and resting on blossoms of Lactuca scariola var. integrata (Asteraceae). It has been reared from a chicken pen.
Milichiella arcuata var. has been collected in wild mushroom traps, “ADg. traps”, mushroom traps [under] Palmetto shrubs (Arecaceae), and Malaise traps. A questionable specimen of this variety emerged from the detritus of a gopher tortoise burrow.
Differs from congeners in the combination of shiny mesonotum, white wings and silvery microtomentose male T2-5.
Male coloration and vestiture: frons subshiny black, ocellar triangle and upper orbital plates shiny black, lunule brown, basoflagellomere black, sometimes basomedially reddish, face greyish microtomentose, palpus black; thorax with mesonotum shiny black, scutellum brown microtomentose, pleura with anepisternum and middle of katepisternum shiny, otherwise brown microtomentose, wing white, veins white, brown spot at tip of vein R1 absent, calypter white, halter yellow, legs black, fore and hind tarsus with yellow brush; abdomen with T2-5 silvery microtomentose. Female coloration and vestiture: halter yellow, abdomen with T1-4 brown microtomentose, T5 shiny.
Morphology. Head: frons with 2+0.8 orbital and 2 frontal setae, anterior frontal seta medioclinate. In males frons 2.2x as wide at posterior margin than at base of antenna, arista about 3.3x as long as basoflagellomere wide, pubescence on arista very short, posterior eye margin with notch (4oc, female: 5-6oc) and slight emargination.
Thorax: 2 dc, 1 prsc, 1 pprn, 1 prs, 2 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 (3.1), and ultimate section of vein M1 1.5x 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, T2-4 posterior margin with 1 row of setulae. S5 2.1x as long as wide, 1.7x as long and 1.3x as wide as S4, setulose on posterior 3/4 except for middle line. Male genitalia with apical seta on cercus as long as longest epandrial setae; dorsal length of epandrium less than in Milichiella lucidula; epandrium with striate anteroventral extension and 0 setae on subepandrial plate, surstylus 0.3x as long as epandrium high, dilated posteroapically (1.4x) with anterior margin straight and slight angle at anteroapical margin, 2.0x as long as wide, structure of lateral surface striate, medial surface without setulae.
Special characters: wings and abdomen bright white, labella shorter than palpus.
Body length: 2.5-3.2 mm; wing length: 2.2-2.8 mm.