The three major suborders are largely characterized by differences in the way silk is used, whether to produce nets or tubes, or as glue to make various types of portable cases, often incorporating sand and small pebbles, or bits of leaves and twigs, the cases varying in design among the different species. Some larvae are free-living and predaceous, but nevertheless lay down a strand of silk as they move, much like the larvae of Lepidoptera. The fascinating nets and cases produced by the larval stages are most familiar to the non-entomologist, and the case making behavior of some species may account for the common name, caddisfly. The Larvae are generally 'eruciform' (caterpillar like) or Campodieform (grub like) and go through a number of instars generally 5 before pupation. They all have gills, a closed respiratory or trachael system ( i.e. they have no spiracles) and a pair of claws at the posterior end of the abdomen. They live and can be found on or under rocks, amongst weeds or swimming free

The eggs are laid in or near water surrounded by a glutinous mass which absorbs water and expands greatly after deposition. Female Caddis flies enter the water either by walking or by diving and cement the eggs to stones or sometimes water plants below the water surface.

Females can stay under the water for more than 30 minutes, the hairs on their body holds a film of air around the body which acts as a physical gill; CO2 diffuses into the water from this air film and oxygen diffuses the other way, the insect spiracles (breathing holes) are never in contact with the water so the insect is effectively still breathing air. This is a technique for breathing under water used by a quite a lot of insects that are basically terrestrial and air breathing.