The bottom of troutstreams in Northwest Wisconsinare loaded with a variety of caddisflies. Most caddisflies build a house of stone, sticks and debris and live the aquatic larva stage in the house. (See photos below for caddis in their cases.) The caddis larva carry their case around with them. Analyzing a trout's diet through it stomach you will probably find an assortment of caddisflies still inside their cases. Trout seem to know that inside those stick or stone houses are food and when nothing is hatching they may feed on them, as well as freshwater snails, crayfish and other aquatic insects.
Caddisflies hatch throughout the Spring, Summer and Fall season. They vary in color and size. 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 freestone streams of Northwest Wisconsin you may see the Grannom (Brachycentrus), or Rhyacophila caddis hatch. Both can cause the trout to start to slash and swirl in a frenzy as they rush to take the fast emerging caddis pupaes. Some written accounts mention that caddis pupaes emerge in a gaseous bubble that aids them in quickly shooting from the bottom to the surface where they quickly emerge as a winged adult and fly off. This is best imitated with Gary LaFontaine's Emergent Sparkle Pupa pattern.
Trout may feed on the caddis cases, digesting the larva and passing the case materials through their intestines. The Strawman nymph was developed to imitate caddis in their case.
These large stick case larvas appears to be family Limnephilidae genus Pycnopsyche (Great Brown Autumn Sedge), which emerge in September or October in Wisconsin. The adult caddis are about 20mm long and have a medium brown 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..