This is a fairly creative assembly, but it is effective on most coastal varieties that feed on shrimp, as well as freshwater species that feed on scud and crawfish. For freshwater, I recommend something other than a stainless steel hook, since if you break off while the hook is still in the fish, stainless will not rust away, increasing chances for mortality.
Hook: 34007 (stainless steel sproat) 8-4/0
Thread: brown kevlar
Legs: brown saddle hackle
Underbody: clear antron dubbing
Overbody: strip of sheet polyurethane (6 mil or heavier preferred)
Feelers: brown horse mane
Eyes: melted monofilament (25 - 50 lb test)
Don't expect to get this fly perfect on the first time. It takes a little experimenting to get the dubbing thickness and the shape of the overbody correct (among other minor problems). The overbody strip should not cover the bottom portion of the fly when the final wrap is made. Some minor trimming can be made before the overbody goes into place, but getting it correct before tying it to the body is by far the better process. Work at a few test runs without the hackle and hair, using a less expensive dubbing, to get the template for the fly for a particular sized hook. Double cut your test runs so that a proper fit has an exact template yet unapplied. The copy can be used to make a template of more durable material for future cuttings.
I've explained the monofilament eyes often enough before, but for newcomers: Take a piece of heavy monofilament 4-6 inches long and place in a pair of hemostats. Light the ends (one at a time) with a lighter and melt them down to a ball. Blow out the flame as it reaches the hemostats. Allow to cool facing downward before touching (both for shape and safety). I make these in large batches in a variety of sizes and store for use as needed. Do this over a safety cover in case there are drips. Do be careful. The potential burns are small but quite severe, usually creating blisters.
Begin with a good solid foundation, for many saltwater species have sharp teeth, and the better the foundation, the longer the fly will last. For the same reason, kevlar thread is the choice for tying, since monocord is too easily cut by their sharp teeth. When the foundation is set with two coats of cement, tie in the horse mane, hackle, over body, and finally the eyes. Dub the antron to the thread (fairly thick), then wrap the hackle to the eye and follow with the dubbing. Tie down and trim the top side of the hackle (but not the sides).Pull the overbody to the eye and stretch. Cut a small hole in the strip so that it slips over the eye. Tie off and wrap the overbody with thread to the hook bend. Finish off with a wrap knot. Trim the overbody flap into the shape of a tail.
Once you get the pattern down, it's easier to make these in batches than it is to produce them singly every time you need one. This is a fly that requires a certain touch to get the right cuts and balance, so it's best to make as many as you'll need for the season in advance and be done with it.
Now, once you get out on the water with these, there are a few tips for using them. These flies work their very best in estuary areas of inland bays where the fish come shallow to feed on the smaller shrimp before they are big enough to take to open water. My best success with these is in areas where two shorelines meet at 90 degress to form a small tidal pool too shallow for fish to penetrate. Smaller shrimp (and fry) will congregate in these pools for safety on the incoming tide, but as the tide goes out, fish will sit off of these areas in deeper water and wait for the currents to empty the contents of these pools in their direction. Trout, red fish, croaker, and especially flounder (along with many other species) are caught in this manner, casting short and letting the tidal current take the fly away from you. An occasional twitch is all you need (if that) to intice the fish into striking. Speckled trout may need a harder jerk, but in most cases, this is one situation where the fast lure is not needed to catch them.
There are many other techniques for using the fly, like in wade fishing the surf. There is more than enough action in the waves and currents to keep this fly active on the drift by their play on the flyline.
These flies may be enhanced with a saltwater scent (shrimp scent, naturally).
This is also a good fly for freshwater where scud live. Generally the fly needs to be scaled down to a 8-14 hook size to be most effective, though the larger ones can work in imitating molting crawfish of some species.