The X-Caddis in size #16 imitates an emerging caddis with its trailing shuck, matching the vulnerable stage trout key on.
Fish it dead-drift in the surface film during caddis emergences. The trailing shuck is the trigger for selective fish.
Restock before your next trip so you are ready the moment fish start rising. Present it with a drag-free drift, mending your line as needed to extend the drift through the feeding lane.