The southern Appalachian Mountains are home to the greatest diversity of Blephariceridae (Dipter ) in North America, with 13 Blepharicera Macquart species inhabiting the region. Sympatric Blepharicera species seem to occupy a common ecological niche, in contradiction to the competitive exclusion principle. Instar IV Blepharicera larvae were studied to determine whether dietary differences facilitate coexistence of sympatric species. Diatom assemblages of Blepharicera diets, total diatom biovolume ingested, and similarity between diatom assemblages of larval diets and the forage base were examined. Dietary characteristics were compared among Blepharicera species within and between discrete microhabitats at 3 sites in southern Appalachia. Data showed broad dietary overlap among species that co-occurred in the same microhabitat and strong microhabitat effects on larval dietary assemblages. In addition, several species ingested disproportionately greater biovolumes of small, adnate and prostrate diatom species compared to their availability on the substratum. Sym- patric Blepharicera species may not partition food resources where spatial overlap is most acute.