Small larvae, up to 3.5 mm long.
Antenna with 4 segments; segment 4 longer than third, both these segments short. Blade bifid, subequal in length to flagellum. Lauterborn organs small.
Labrum with SI simple or weakly serrate. Remaining S setae simple and fine. Pecten epipharyngis consisting of 3 fine spines. Chaetulae laterales and basales present. Premandible with 2 subequal, pointed, apical teeth and 1 broad rounded inner tooth; brush absent.
Narrow, pointed, apical tooth longer than combined width of 3 inner teeth. Seta subdentalis long and narrow. Seta interna with some pectinate branches. Whole mandible strongly curved inwards.
Mentum with single median tooth with median nipple; 6 pairs of pointed lateral teeth. Ventromental plate small, not extending beyond outer tooth of flattened mentum; beard absent.
Maxilla palp length is unique amongst described Orthocladiinae larvae, resembling that of Tanytarsini. Terminal seta and bisensillae well developed, with long seta basally. Pecten galearis absent. Setae maxillaris small.
Body with anterior and posterior parapods present, divided and bearing claws. Procercus like Pseudorthocladius in bearing 1 elongate anal seta, 1/2 the length of the body. Anal tubules shorter than posterior parapods, without constrictions.
Larval Krenosmittia originally were described as krenophilic (living in springs) in the boreal northern latitudes. However exuvial findings show that some species are found further south, and in rivers and lakes. Nearctic exuviae are found in low to middle order streams. Furthermore species are found in Afrotropical and s.e. Asian streams and rivers.