1a: Body of larvae very curved and case snail shell-like.--Helicopsychidae
1b: Larvae not curved. Cases in other shapes or case less.--Go to 2
2a: Each thoracic dorsum covered by large paired plates.--3
2b: Dorsal part of each meso and metathoracic segments with large areas of membranous cuticle on at least the last thoracic segment (metathorax). (A: Entirely membranous meso and metathorax. B: Large plates on mesothorax and small plates on metathorax.)--4
3a: Abdominal gills many branched. Mature larvae greater than 6 mm long. Larvae build retreats attached to rocks or other debris rather than cases.--Hydropsychidae
3b: Mature larvae less than 6 mm long. Gills single or not evident. Cases are made of a variety of materials including, sand grains, silk, and algae.--Hydroptilidae
4a: Antennae "long", about 6 times as long as wide.--Some Leptoceridae
4b: Antennae much shorter and indistinct.--5
5a: Plate on prothorax large. Meso and metathorax membranous or if plates are present they are very small.--6
5b: Plates on prothorax and mesothorax large and well developed.--11
6a: Abdominal segment one has a dorsal hump and lateral humps. (d.h.= dorsal hump;l.h.= lateral hump; mes= mesonotum; met= metatnotum).--Phryganeidae
6b: No humps on abdominal segment one.--7
7a: Anal proleg short and broadly joined with abdominal segment nine. Claw with one or more dorsal accessory hooks .--Glossosomatidae
7b: Anal proleg longer and not broadly joined to segment nine.--8
8a: A plate present on dorsal surface of abdominal segment nine. Branched gills present or absent.--Rhyacophilidae
8b: No plate on abdominal segment nine. Gills never branched.--9
9a: Upper lip of mouth (labrum) in the form of a "T".--Philopotomatidae