Caddis comprise 93% of all the aquatic biomass in our own Lower Sacramento River.
There are about 12,000 known kinds of caddis (tricoptera). Old-timers call them sedges. The insect is closely related to moths and butterflies, but all caddis begin their lives in the water. They're tougher and can survive in less pristine water than mayflies. Maybe that's why there are so many of them and why they're so important in the trout diet.