Large, pale red to red, up to 18 mm long. With 2 pairs of widely separated eyes. Head dorsoventrally flattened, apically narrow, wedge-shaped. retractible into thorax. Thoracic segments strongly thickened.
Frontoclypeolabral apotome present, lateral labral sclerites indistinct.
Antenna with 5 segments. Lauterborn organs minute opposite on apex of segment 2, with style. Ring organ in basal half of segment 1, seta present. Blade very broad, extending to apex of 2nd segment of antenna, accessory blade large, about half length of blade.
SI and SII slender and short, distally plumose; SIII slender, relatively long, simple or distally plumose; SIV normal. Seta premandibularis simple. Labral lamellae represented by 2 platelets with long distal teeth. Chaetulae and spinulae simple, in part broad, lamellate. Pecten epipharyngis comprising 10-20 slender long, simple, or distally divided lamellae. Premandible with 3 teeth and strong brush.
Broad, triangular, distal half black. Dorsal tooth absent; apical tooth and 2 inner teeth and ridge with 2 teeth. Pecten mandibularis and seta interna absent. Seta subdentalis simple, very slender, short.
Mentum with toothed edge of 10-20 teeth, usually worn flat, with ventromental plates reduced to a minute striated part beneath outermost lateral tooth. Setae submenti long, simple.
Slender, becoming narrower anally. Posterior parapods very short, claws directed backwards. Procercus absent. Anal setae seated directly on body; procercus absent. Lateral and ventral tubules absent. Anal tubules large, parallel to longitudinal axis of body, projecting backwards.
The mining larva of Stenochironomus is recognizable by the dorsoventrally flattened head which tapers to a "chisel" shape anteriorly, in combination with the concave mentum and almost completely reduced ventromental plates. In addition the thoracic segments are always strongly thickened and the posterior parapods and procerci are reduced. Differentiation from Australasian Harrisius depends upon subtle difference in ratio of antennal segment lengths, and the complete absence of any striae or spines on the scarcely recognizable ventromental region in Harrisius.
Larvae of Stenochironomus are obligate miners in living and dead vegetation, including woody parts of plants.
The genus has a worldwide distribution, from temperate zones to the tropics. About eleven species occur in the Nearctic, about seven in the Palaearctic. The greatest number of species is to be expected in tropical South America.