Medium-sized to large larvae, to 13 mm long. Red.
Frontoclypeal apotome present, isolated labral sclerite 2, labral sclerites 3 and 4 fragmentary.
Antenna with 5 segments. Ring organ in mid-1st antennal segment. Lauterborn organs opposite on apex of 2nd segment. Antennal blade not extending to flagellum apex, accessory blade about 1/2 as long as segment 2. Style on apex of 2nd segment, about as long as segment 3.
SI seta slender, plumose on each side; SII simple; SIII short, simple, slender; SIVa simple sensillum. Labral lamellae normal. Field of short spinules between SI and labral lamellae. Pecten epipharyngis simple, of c.15 small teeth, middle one strong followed by alternate short and long teeth to either side, without surface toothlets. Premandible with 2 long slender teeth, brush strong; seta premandibularis simple.
Mandible with strong pale dorsal tooth, with smaller tooth attached basally, apical tooth dark, with 3 pointed inner teeth. Seta subdentalis simple, strongly broadened from slender base, extending to base of apical tooth. Seta interna of 4-5 plumose branches. Pecten mandibularis with toothed lamellae. With about 10 radially-arranged striae or furrows on outer surface.
Mentum with domed median tooth with minute outer toothlets almost completely fused, 6 pair of laterals, regularly decreasing in size to 4th laterals smaller than 3rd or 5th. Ventromental plates separated medially by width of median tooth, about equal to width of mentum, with numerous fine striae across entire surface.
Without lateral or ventral tubules.
Fleuria larvae are very similar to those of Chironomus. They lack, however, the two pairs of ventral tubules. In addition, the median tooth of the mentum is very broad and only weakly indented laterally, not trifid. A good character is the small field of spinules between the labral lamella and the SI setae, which is lacking in all Holarctic species of Chironomus.
Larvae of Fleuria inhabit soft sediments of shallow, productive ponds (fish ponds, seashore lakes) and tolerate slightly brackish water.
Monotypic genus with F. lacustris occurring in central and eastern Europe.