I often catch large trout on ants when they refuse to take the fly which matches the aquatic insects, even when there is a good hatch of aquatic insects. I use ant patterns on the native brook trout streams in Virginia from April to September. They are very productive on trout streams in PA, NC, NY, and in the Rockies. Artificial black ants are effective when you get a natural drift, but they can be hard to see on the water. I use a Mr. Rapidan Ant because the yellow wings help me see it on the stream.
If a trout comes up and looks at your size 14 and refuses it, taper your leader down to 7X and drift a size 18 pattern over him. This seldom lets me down. The trout you see rising close to the stream banks will often take a dry ant on your first cast.
Tying Materials for Mr. Rapidan Ants
Hook: Mustad Signature 94840 or Heritage R50AP Dry Fly hook sizes 14, 16, 18
(size 16 included in kit)
Thread: Black 6/0 Prewaxed Nylon
Body: Black Fly Rite
Hackle: Metz Graded Hackle Single Pack in Grizzly (size 16 included in kit)
Wing: Yellow calftail (you could also use calf body hair in yellow)