Medium-sized larva, up to 8 mm long. Head capsule oval; cephalic index 0.60-0.65. Dorsally, S5, DP, S8 and S7 almost aligned, S8 and S7 and DP evenly spaced. Ventrally eye-shaped VP bigger than setal sockets, situated between S9 and S10 and anterior to SSm-S10; pits of S9 and S10 smaller than SSm. All setae simple verify, S10 stronger than S9.
Rather short, <2x as long as head, 2.5x as long as mandible. Antennal ratio about 4. Basal segment about 9x as long as basal width, with ring organ at base of apical 1/2; segment 2 about 9x as long as wide; segment 3 about 4x as long as wide, as long as terminal segment. Style cylindrical in basal 1/2, with thickened wall; apical 1/2 broadened, club-shaped, hyaline, extending beyond middle of terminal segment. Blade ending at level of segment 3; basal ring 4x as high as wide. Accessory blade extending somewhat beyond blade.
Strongly curved and gradually narrowed towards apex. Apical tooth almost 2.5x as long as basal width, 1/4 length of mandible. Inner tooth large and blunt; mola weakly expanded, with hump-shaped accessory tooth near base long seta subdentalis; Ventrolateral setae situated on outer margin of proximal 1/2 of mandible; seta 1 short peg, 2 and 3 simple; distance between ring organ and seta 3 somewhat less than that between setae 3 and 2.
Basal segment of palp 3.5x as long as wide; with ring organ at base of apical 1/2.
Without fringe of swim-setae. Anal tubules spindle-shaped, about 4.5x as long as wide. Procercus brown, about 4x as long as wide, with 7 brown apical setae. Claws of posterior parapod darkened, all simple; larger claws with small spines on inner and/or outer margin.
Hudsonimyia is a Pentaneurini, resembling Pentaneura in the adult male and some larval features, but differing in the pupal stage. Major differences from Pentaneura are the low molar area, lack of tubercles at bases of strong supra-anal setae and rather different ventral and dorsal cephalic setae and pits. Hudsonimyia has a more strongly curved, sturdy mandible relative to Trissopelopia, in which the mandible, antennae and palps are strongly elongate. Somewhat similar Larsia and Zavrelimyia possess a molar tooth larger than that of Hudsonimyia. Other aids to recognition include the yellow-brown to brown posterior 1/2 of the head and claws. Following Caldwell et al. (1997) and Epler (2001a), the relegation of Hudsonimyia to subgenus status in Pentaneura Philippi by Sublette and Sasa (1994) is not accepted here.
The two nearctic species H. karelena and H. parrishi may be separated by colour: the head capsule and posterior parapod claws of H. parrishi are yellowish brown; the head capsule and posterior parapod claws of H. karelena are brown, with the posterior portion of the head capsule usually contrastingly much darker than the anterior (Epler, 2001a).
Larvae of both nearctic species live in algal mats of more or less hygropetric habitats with slow to moderate flow in eastern North America (Roback 1979a, Caldwell and Soponis, 1982a). Hudsonimyia vittaria was described from Guatemala: the immature stages may have been misassociated with the adult.