Short‐term static bioassays were conducted in duplicate to determine sublethal effects of fluoride in soft water (hardness average value of 15.6 mg CaCO3/I) to larvae ofHydropsyche bulbifera, H. exocellata, H. lobata, H. pellucidulaandChimarra marginata(Trichoptera, Insecta). Last instar larvae of each species were exposed to 5–6 different concentrations of sodium fluoride (NaF) for 4 days. In addition, sodium and conductivity toxicity controls were performed with sodium chloride (NaCl). Compared with control larvae, animals exposed to NaF exhibited two main toxic effects before dying: (1) a migration from their retreat and capture nets (96 hours EC50 values were 19.2, 21.3, 34.8, 24.6 and 33.5 mg F‐/1 respectively) and (2) a protrusion of their anal papillae (96 hour EC50 values were 18.9, 20.5, 33.9, 23.5 and 108.5 mg F‐/1 respectively). Most protruded anal papillae were darkened inHydropsychespecies, the percentage of darkened anal papillae increasing as the fluoride concentration was higher.H. bulbiferaandH. exocellataappear significantly(P <0.05) as the most sensitive species to NaF. It is concluded that these sublethal effects were fundamentally due to fluoride ions (F‐).