Small, red, up to 5mm long. Head rather bean-shaped in lateral view.
Frontal apotome without frontal pit, anteriorly separated from narrow clypeus by straight suture; labrum and labral sclerites uncertain.
Antenna with 5 segments. Basal segment shorter than flagellum. Lauterborn organs not visible, or present opposite on apex of segment 2, well-developed style apical on segment 2. Ring organ in basal 1/4 of segment 1, seta absent. Blade broad, shorter than antennal flagellum, accessory blade short and slender.
SI plumose distally; SII simple; SIII slender, as long as SII; SIV relatively large. Seta premandibularis long and simple. Labral lamellae of 6 isolated toothlets. Pecten epipharyngis trifid, consisting of 3 basally fused toothlets. Premandible with 3 teeth and strong brush.
All teeth pale, dorsal tooth moderately developed, broad tooth present subapically on inner side, with long, slender apical tooth on different plane to 4 inner teeth. Pecten mandibularis absent. Seta subdentalis slender, long, weakly sinuous curved and extending beyond outermost mandibular tooth. Seta interna absent.
Mentum pale, with ventromental component of 4 teeth, with smaller median teeth, 5 lateral dorsomental teeth on an even slope and evenly decreasing in size laterally. Ventromental plates separated medially by half width of ventromentum. Ventromental plate about 1.5 times width of mentum, striae only on basal half of plates. Setae submenti simple, very long and strong, situated deep on mentum.
Lateral and ventral tubules absent.
The very small Nilothauma larva is recognizable by the pale mental and mandibular teeth. Distinguishable from the similar larva of Pagastiella by the contiguous eyes, characteristic mentum, very short basal antennal segment and unusually broad antennal blade. In addition the ventromental plate is striated only over the posterior part and the mandible possesses only a single, broad dorsal tooth.
The only European species, N. brayi, has usually been falsely placed in the exclusively Afrotropical Kribioxenus.
Larvae of Nilothauma inhabit littoral and sublittoral soft sediments of lakes. Also found in flowing waters.
Four species are known from the Holarctic, distributed from temperate latitudes to subtropics. Species are known from the Afrotropical, Oriental and Australasian regions.