GRANBY, Colo. — Its not a plague of locusts, but the action on rivers and streams reach a feverish pitch when grasshoppers appear. “You’ve got the dog days of summer when hopper season is happening.

guides these days, Tom Sadler likes to boost his clients’ chances of catching trout by having them fish with two flies instead of one. He sets them up with the kind of rig known as dry dropper: one ...