The two larval species most imitated by anglers are Rhyacophila (green caddis or green rockworms) and Dicosmoecus (October caddis). However, the effort may be misplaced because these are not the caddis larvae most consumed by trout.
Rhyacophila are common in extremely fast riffles on medium-sized streams, and while trout sometimes feed heavily on the larvae, it’s usually during the low light conditions near dawn and dusk. Most anglers cast imitations in water that is too slow or during the wrong times of the day.
Green rockworms (green caddis larvae) draw a lot of attention from anglers, perhaps because they have a common, recognizable name. The attention is unwarranted, and should be directed to other green colored larvae, especially netspinners ( Hydropsyche) in our area. Nonetheless, a nymph box without green rockworm imitations is like a golf bag without a sand wedge: when you need one, you really need one.