Sedge flies are known as Caddis flies in North America, there are about 12,000 species worldwide with about 190 in the UK. Most of those in the UK are too small for anglers to make artificial imitations. The latin trichoptera translates to "hair winged", describing the hairy, moth-like wings.
The fertilized eggs are laid at the surface of the water or on aquatic vegetation protruding above the surface of the water.
Sedge fly larvae make open-ended cases for themselves out of pieces of vegetation, small stones, sticks, or whatever else they can find all bound together with silk. The head and upper abdomen will protrude from the case which is pulled along serving as a retreat from danger. Not all Sedge flies make cases, some stay on the bed and construct their retreat there, sometimes with a net which serves as a food trap. Others make no kind of shelter or case at all until they pupate but crawl around amongst the stones. The larvae feed on algae, aquatic plants and the larvae of other insects.
After about a year those larvae with cases or retreats will secure themselves to something solid and seal themselves inside. Those without cases spin cocoons of for pupation. It takes two to three weeks for pupation after which the pupal sedge fly will cut through its cocoon and swim to the surface. At the surface the pupal skin will split and a winged adult emerges.
Many adult sedge flies can fly immediately, they will mate and die within a few weeks, with the whole life cycle lasting little more than a year. Most of them don't feed either, females return to the water to lay their eggs. The adult flies have four wings, which fold over their backs like a moth, and no tail.