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The long-horned caddisflies comprise 1 of the 3 largest families in the order with about 1,800 described species. The family is about equal in diversity to the Hydropsychidae and only surpassed by the microcaddisflies, Hydroptilidae, in total known species richness. In all of these families, many more new species assuredly await discovery and description, especially from tropical regions around the world. The family was first established by Leach (1815) and includes several species described by Linnaeus in Systema Naturae, 10th ed. Nineteenth century workers also included species now in Odontoceridae, Molannidae, Calamoceratidae, and Beraeidae in Leptoceridae, but by the early 20th century modern family concepts were for the most part established. Over Forty-five genera are known at present in the family, but new genera are still being described. Two genera in particular are widespread and diverse on all continents, Oecetis McLachlan with about 400 described species and Triaenodes McLachlan with about 230 known species.
Larvae of the family construct a wide diversity of cases, perhaps the most diverse in the order. Cases are fundamentally tubular, but can be made entirely of silk secretions, of plant pieces arranged spirally or laid transversely, or of large leaf fragments to form a flattened case. Others make simple tubular cases of sand grains, strongly or only slightly tapered towards the posterior ends; sometimes there are larger stones placed laterally. Mystacides larvae incorporate long conifer needles or leaf stems that trail off the end of the case. Some genera make irregular cases of plant fragments, while others hollow a twig or use the abandoned cases of other caddisflies as their own. Some Ceraclea build flat, limpet-like cases of sand grains, while those that feed on freshwater sponge incorporate sponge pieces and spicules in their cases. The larvae of Leptecho helicotheca Scott from South Africa build snail-shaped cases remarkably similar to those of Helicopsyche. Larvae are found everywhere, from high mountain torrents, through all orders of streams, to large lowland rivers. In northern latitudes, they are common in lakes and in the tropics they occur in oxbow lakes and other standing waters, even temporary ones; some are semi-terrestrial and inhabit the sides of waterfalls where they are wet by the splash. Larvae feed as leaf detritus shredders, periphyton scrapers, and predators, even on freshwater sponge. Adults are often very abundant and come to lights by the 1000s. Their long, slender antennae and generally narrow forewings are distinguishing features. There are quite a few genera that have brightly colored and iridescent hairs and scales on the wings, making them among the most beautiful of caddisflies. (From Holzenthal et al., 2007)