Caddisflies hatch throughout the Spring, Summer and Fall season and are a major source of food for trout. They vary in color, size and emerge at different times of the day and night. Some of the largest caddisflies, such as the Great Brown Sedge (Pycnopsyche) are over an inch long and emerge at night during the Summer. In the Spring on the Northern Wisconsin trout streams it is common to see several different Brachycentrus species emerge, such as the Grannom (darker olive body with a dark brown wing, size #16) or the Apple Caddis (very light tannish colored wing with an apple green body, size #16).
The bottom of freestone streams in Northwest Wisconsin contain a wide variety of caddisflies. Since northern Wisconsin trout streams are surrounded by woodlands the dominate caddisflies are the leaf shredders, algae scrappers and some net builders. This is why you will find many caddisflies larvaes living along the bottom in houses built of stone, sticks and debris. (See photos below for caddis in their cases.) The cased caddis larva carry their case around with them as they crawl along the bottom of the river. Analyzing a trout's diet through it's stomach you will often find a lot of leaf and stick debris along with body parts from caddis larvae. Trout seem to know that inside those stick or stone houses is food. When nothing is hatching trout often feed on them, as well as freshwater snails, crayfish and other aquatic insects found along the bottom of the river.
The net spinning caddis larva prefer the faster water and in riffles where they can collect the food in their nets. There are also free living caddis larva that don't build a house to live in. The Rhyacophila (Green Rock Worm) is probably the best known caddis larva which freely moves around the bottom crawling among the crevices between the rocks.
Eventually the larva seals it's case off and pupates into an adult. When the pupation is complete the caddisfly emerges from it's house as an adult, not a pupae. This is actually referred to as a pharate stage, which means the adult caddis is encased inside the transparent pupal skin or some sort of natural covering and has to find it's way now to the surface. Some written accounts mention that caddis create a gaseous bubble inside their natural covering to aid them in quickly rising from the bottom to the surface. This could explain the silvery glow that some describe accompanies the rising insect. Once arriving at the surface the caddis has to break through the menicus and crawl out of it's pupal skin / covering before flying off to the trees and bushes. Often times the trout are feeding at the surfaces on something we can't see which may be the caddis trying to break through the menicus.
Later after some days in the trees and bushes the caddis adults will come back to lay their eggs. Some lay their eggs along the river, some lay their eggs on branches above the river, some crawl/swim/dive into the river to lay their eggs along the bottom and some drop their eggs from the surface of the river. During the summer months the oviposting generally occurs in the cool of the evenings, while in the Spring it may be during the day. Only the caddis that go back into the river or drop onto the water to lay their eggs are available for the trout to feed on.
Below are some caddisfly photos I have taken over the years in northwest Wisconsin.
These large stick case larvas may be Hydatophylax argus, the Giant Cream Pattern-Wing Sedge which emerges during the summer nights. It has a cream colored body and light colored wing. There is also another very large caddisfly in the family Limnephilidae genus Pycnopsyche (Great Brown Autumn Sedge), also called the October Caddis, which emerge in September or October in Wisconsin. The adult caddis are about 20mm long and have a burnt orange colored body and a brownish mottled wing.
Notice the green body of this size #16 tannish wing caddisfly. These caddisflies emerge sporatically throughout the days in May in many northern Wisconsin troutstreams. The body is more of a size #18 and the wing is a size #16, which is typical of caddisflies. A CDC and elk is an excellent for this.. See photo below..