Beginner’s Fly Tying: Dark Cahill

View our instructional video for tying this fly. This video includes several chapter markers so you can easily jump to the section you wish to view — visit our YouTube channel to easily jump to the chapter of your choice. Written instructions for each fly are presented below.

The fly pattern which I have chosen for the March Beginner’s fly tying is the Dark Cahill dry fly. First, a brief history of the Cahill fly pattern. In the 1880’s a New York railroad worker named Daniel Cahilldeveloped a fly that became famous all over America, the Light Cahill. When he wasn’t fishing or tying flies, he was a brakeman on the old Erie and Lackawanna Railroad. While the Light Cahill is a great general imitation of summer mayfly duns, a variant of this the Dark Cahill is a great imitation of some of the spring mayfly duns.

In our Beginner fly tying series, our participants have tied a spectrum of fly patterns ranging from nymphs, wet flies, streamers, terrestrials, worms, etc. Each pattern was chosen for our sequential monthly tying sessions to provide the beginner with an understanding of how to use and apply different materials in fly composition, integrated with basic techniques for tying a spectrum of fly imitations of natural fish foods. The Dark Cahill will be the first classic dry fly pattern which our class will learn to tie since our series began early in 2020. And while the Dark Cahill dry fly is most likely outside the “top ten” beginner fly patterns endorsed on the internet, the tying steps and technique used in creating this fly are perhaps simpler to perform, albeit virtually the same, regardless of which mayfly dun imitation a fly tier would pursue. Written instructions are provided below.

Dark Cahill

Step-by-Step Instructions for Tying the Dark Cahill


  • Hook- Standard dry fly hook – sizes 10-14
  • Abdomen – Muskrat (grey) dubbing (with or without) antron
  • Tail- Brown neck hackle
  • Wing – wood duck flank feathers (or dyed mallard flank)
  • Hackle- brown neck hackle
  • Thread – brown preferred (6/0)

Tying Procedure

  • After pinching down the barb on the hook, insert in vise. Start the thread approximately 1/3 distance to the rear of the hook from the hook eye. Make several wraps to lay down a single base layer of thread, stopping about mid shank and return back to the initial location where the thread was started.
  • Select a single wood duck flank feather (preferably one with round tip of fibers). Remove the fluffy butt end of the feather. Then stroke the tip forward and hold the feather in your left hand and measure the length of the tip section against the hook shank. This tip section should be no more than the shank length (i.e. you are using the shank as your measuring tool).
  • Still holding the feather in your left hand move your hand forward such that the tip section is forward from the location where the thread is hanging. Make 2-3 wraps of thread exactly at that location to secure the feather tip in place. Then make addition thread wraps to the rear of the tie-in location.
  • Lift the butt section up at a 45 degree angle and clip off the butt section laying the scissors flat (parallel) to the hook shank.
  • Continue making thread wraps over the sloped section of the feather butt. Then return the thread wraps forward to the initial tie-in point.
  • Using your left hand lift the feather tips up to 90 degrees from the shank and make a number of thread wraps immediately in front of the feather tip, which should secure the tip in an up-right position.
  • Once the feather tip is held in place advance thread wraps toward the rear of the hook stopping at the hook bend.
  • Next select one medium size rooster hackle. Flair the hackle fibers 90 degrees to the hackle stem and then quickly cut/jerk the fibers (approximately 10 fibers) loose. Transfer this fiber bundle to the right hand to measure ~= shank length.  Tie in at the hook bend, first with several loose wraps, followed by tight wraps forward. Trim off any excess hackle butts immediately behind where the butt section of the wing was tied in.
  • Thread should be hanging at this junction. Dub a ~2” section of the thread with the muskrate grey dubbing, leaving ~1/4 of open thread. Wrap the dubbed thread toward the bend laying down a dubbed section of the body forward to the wing. Stop thread wraps slightly behind (1/16”) the wing.
  • Tie in 1 neck hackle feather which was previously chosen consistent with the hook gap size. Trim ~1/8”-1/4” of fibers off the butt end of the hackle feather. (The thread should be hanging immediately behind the wing). Hold the feather along the tier’s side of the hook with the trimmed section facing forward toward the hook eye. Secure the feather with several wraps behind the feather-wing tip and several forward of the wing.
  • Leave the thread bobbin in place slightly behind hook eye.
  • Using hackle pliers begin making ~3 wraps of hackle behind the wing and 2-3 in front of the wing. Hold the hackle fibers back with your left hand and secure the tip of the hackle with several thread wraps. Clip off the excess feather and whip finish the fly head. One drop of head cement/UV cement to finish off the fly.  

By Don Fine