The Trichoptera are mid-sized, moth-like insects with two sets wings. They may vary in colour from orange to tan to green, and often appear to be hairy.

Caddisflies are best known for their building skills in their aquatic larval stage. Young caddisflies construct casings from a variety of materials including sand, gravel, plant debris, and sticks. These cases provide the larva with protection and camouflage until it is fully grown. Cases vary greatly in appearance depending on species and availability of materials. Although most caddisflies do construct these well-known cases, there are some exceptions such as the free-living caddisflies (Rhyacophilidae), of which only two known species are found in the NWT.

After a pupating phase, caddisflies emerge from the water as fully grown, winged adults. In some areas, the onset of cooler weather triggers this emergence, ensuring that all caddisflies become active mating adults at the same time. After mating, eggs are laid underwater by the female. Caddisfly eggs will not hatch unless exposed to moisture. Most species have a life span of roughly one year, however, in cooler climates caddisflies may over-winter as pupae, or as eggs as they require more time to fully develop.

Due to its significant aquatic stage, caddisflies provide a good indication of water quality and ecosystem health. Adult caddisflies are important food sources for a number of animals such as fish, bats, birds, and amphibians.

There are 122 species of caddisflies confirmed present in the NWT.