“Caddisfly larva” by jmw975 is licensed under CC BY-NC-SA 2.0

Most caddisfly larvae look like inchworms and build themselves cases, or houses, to live in. Different species build their cases with different materials—some species use sticks, others use leaves, and some use sand or tiny pebbles. Many also spin nets which they use to collect food from the stream. Most caddisfly larvae cannot tolerate water pollution, and can only live in clean water.