Isonychia mayflies, often known as slate-wing or mahogany duns, are prevalent throughout the Eastern United States, plus, the nymphs are active for most of the fishing season. That means an Iso nymph is a good searching pattern if you can't tell what the fish are feeding on. These are predatory "swimmer" nymphs, which means that you don't want to dead-drift them. Instead, use short strips to move the nymph from the middle of the current toward the bank. Trout will often chase down these speedy nymphs, which means that they don't inspect the fly as much as they would a dead-drifting pattern, plus you don't normally need to go with an ultralight tippet. Stripping or swinging this nymph through a run prior to an emergence can be very productive.

In this great video from Tightline Productions, Matt Grobert ties Vinnie's Isonychia Nymph, named for his friend Vincent Caffarra, who developed the fly. As usual, Grobert, an author and blogger, demonstrates some useful tying tips. I especially like the way he protects the space behind the hook eye by wrapping the thorax dubbing rearward.

Vinnie's Isonychia Nymph from Tightline Productions on Vimeo.

 

          Vinnie's Isonychia Nymph
          Hook: 2X-long, heavy-wire nymph hook (here a TMC #5262),
                     sizes 10-14.
          Thread: Black, 6/0 or 140 denier.
          Tail: Peacock herl, 3 swords.
          Rib: Copper wire, small.
          Back stripe (optional): Stripped quill of wood-duck flank feather.
          Dubbing: Blended rabbit fur—2 parts claret, 1 part brown,
                           1 part black.
          Wing case: Dark turkey-tail segment.
          Thorax: Blended rabbit fur, as above.
          Legs: Olive brown hen-back feather.
          Head: Black tying thread.

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