Medium-sized larvae, up to 5 mm long.
Antenna with 4 segments; 4th segment longer than 3rd. Blade extending beyond apical segment by a variable distance. Lauterborn organs absent. Style present subapically on segment 2.
SI simple or lanceolate, more laterad than usual; SII elongate, apically pectinate, arising from tubercle, SIII simple or plumose, anterior to SII; SIVa and b well developed. Labral lamellae absent. Pecten epipharyngis consisting medially of 3 slender, needle-like spines with 3 similar shaped and 4 broader chaetulae laterales. Premandible bifid; brush absent.
Apical tooth longer than combined width of variable number of inner teeth; only innermost tooth completely separated; further inner 2 teeth indistinctly separated from mola. Seta subdentalis distinctly shaped. Seta interna present, with only simple branches.
Mentum strongly curved such that only median group of 6 (possibly 7) teeth are visible in uncompressed larvae; 5 pairs of later teeth on each side of paler median area. Ventromental plate distinct, not extending beyond outer tooth of flattened medium; beard absent.
Maxilla with elongate palp. Numerous serrate and simple setae maxillaris.
Body with divided parapods bearing claws; those on posterior parapod divided into fine or stout types. Procercus large, slightly higher than wide; 6 or 7 anal setae of different length present, the longest up to 1/4 of body length. Only 1 pair of anal tubules present, conical in shape and shorter than posterior parapods. Body with thick covering of stout setae otherwise seen only in Abiskomyia.
Larval Epoicocladius live externally on the bodies of nymphs of mayflies, on Ephemera danica in the Holarctic and Hexagenia in the Nearctic. There are two species in North America, of which Epoicocladius flavens (Malloch) appears to be Holarctic in distribution.