Small to medium-sized larvae, up to 5 mm long.
Single sclerite anterior to frontoclypeal apotome.
Antenna with 5 segments: 2-5 short and subequal. Blade subequal to flagellum. Ring organ small, near midpoint of 1st segment. Lauterborn organs not distinguishable. Style arising subapically on 2, extending to apex of 3.
SI lanceolate with 2-4 lateral branches, SII stout, lanceolate, SIII very fine, SIV longer than usual, a simple seta without SIVB. Pecten epipharyngis of 3 rounded scales. Premandible with 4 distinct teeth; with strong brush.
Mandible with apical tooth shorter than combined width of 4 inner teeth, 4th not well delimited from mola. Seta subdentalis small, short and blunt, not extending beyond mola. Seta interna well developed, with 6-7 finely plumose branches.
Mentum with 2 median teeth and 5 pairs of lateral teeth, decreasing evenly on slope. Ventromental plate barely developed; beard absent.
Anterior parapods apparently fused, with fine spinules and claws with fine inner serrations. Posterior parapods separate with simple claws. Procercus probably absent, but with 4 strong, short anal setae in cluster. Anal tubules uncertain. Body without distinct setae.
Belgica is a monotypic Antarctic genus based on B. antarctica. In Wiederholm (1983) it is inferred that the larva resemble those of the marine genera Tethymyia and Thalassosmittia. Although the bodies are similar, this is not so for cephalic features, as shown by Usher and Edwards (1984). Belgica has a premandibular beard, lacking in other marine orthoclad genera, and lacks labral lamellae, present in others. Furthermore the mentum structure differs: Belgica has a double median tooth and five pairs of laterals: in contrast, Tethymyia and Thalassosmittia have a single median tooth and four pairs of laterals.
The biology of Belgica is well known due to the amount of Antarctic research on anything that moves. Larvae of Belgica are found quite widely in the maritime Antarctic, living in damp soil beneath Deschampsia and Colobanthus plants, and perhaps associated with enrichment such as penguin guano. Belgica antarctica is the most southerly holometabolous insect (68.17'S, Usher and Edwards, 1984).