Caddisflies are not really flies. True flies are members of the insect order Diptera. They have one pair of wings.
Caddisflies are in the insect order Trichoptera. They have four wings. The front pair is often a little longer than the back pair. The wings are usually hairy. This is the reason their order is called Trichoptera, it's from Greek words that mean “hairy wings”.
Caddisflies live near ponds and streams. They develop in a four-stage process called complete metamorphosis. The stages are egg, larva, pupa, and adult.
Female caddisflies deposit their eggs in the water or very near the water. When the larvae hatch, they live in the water. They breathe with gills. Some larvae are predators. Many larvae are scavengers.
Most caddisfly larvae make cases out of silk that they spin. They camouflage the cases with twigs, gravel, sand particles, and debris. Some larvae use hollow sticks as cases.
The larvae live in the cases and use them as shelters. They carry the case with them as they walk around on the bottom of the pond. As they grow, the larvae add onto the cases.
Many people spend time looking for caddisfly larvae in streams and ponds. They recommend it as a way to develop patience. They report that one must remain very still while watching for the larvae. The larvae do not move until all the fish have passed by. When there are no predators, the larvae move around the bottom of the stream.
When it is time for the larvae to change into adults, they seal them selves inside their cases. They complete the pupa stage inside the sealed case. The larvae that develop at the end of the summer often spend the winter inside the case. These larvae change into adults during the following spring.
When the caddisfly has finished changing from a larva into an adult, it breaks out of the sealed case. It climbs or swims out of the water. Many caddisflies complete their life cycles at the same time. There are often hundreds of new adults swarming around the pond. They are active in the evening. They spend their time seeking mates or flying to the lights of homes and buildings that are near the pond.